java开发想必是很熟悉StringBuffer和StringBuilder这两个类了，今天我们就深入了解这两个货是怎样的
提神做正事表情包
public final class StringBuffer
extends AbstractStringBuilder
implements java.io.Serializable, CharSequence{
/......./
}
public final class StringBuilder
extends AbstractStringBuilder
implements java.io.Serializable, CharSequence{
/......./
}
StringBuffer和StringBuilder都继承了AbstractStringBuilder同时实现了Serializable, CharSequence
//下面是StringBuilder的构造器
public StringBuilder() {
super(16);
}
public StringBuilder(int capacity) {
super(capacity);
}
public StringBuilder(String str) {
super(str.length() + 16);
append(str);
}
public StringBuilder(CharSequence seq) {
this(seq.length() + 16);
append(seq);
}
//下面是StringBuffer的构造器
public StringBuffer() {
super(16);
}
public StringBuffer(int capacity) {
super(capacity);
}
public StringBuffer(String str) {
super(str.length() + 16);
append(str);
}
public StringBuffer(CharSequence seq) {
this(seq.length() + 16);
append(seq);
}
//下面是AbstractStringBuilder的构造器
AbstractStringBuilder() {
}
AbstractStringBuilder(int capacity) {
value = new char[capacity];
}
从上面的代码可以知道数据并是储存放置在他们的父类属性
value里的，对数据的增删改查其实都是StringBuffer和StringBuilder调用AbstractStringBuilder里面的方法实现的
问题来了？StringBuffer和StringBuilder有什么区别呢
不说废话先看源码
StringBuffer类：
@Override
public synchronized int length() {
return count;
}
@Override
public synchronized int capacity() {
return value.length;
}
@Override
public synchronized void ensureCapacity(int minimumCapacity) {
super.ensureCapacity(minimumCapacity);
}
@Override
public synchronized void trimToSize() {
super.trimToSize();
}
@Override
public synchronized void setLength(int newLength) {
toStringCache = null;
super.setLength(newLength);
}
@Override
public synchronized char charAt(int index) {
if ((index < 0) || (index >= count))
throw new StringIndexOutOfBoundsException(index);
return value[index];
}
@Override
public synchronized int codePointAt(int index) {
return super.codePointAt(index);
}
@Override
public synchronized int codePointBefore(int index) {
return super.codePointBefore(index);
}
@Override
public synchronized int codePointCount(int beginIndex, int endIndex) {
return super.codePointCount(beginIndex, endIndex);
}
@Override
public synchronized int offsetByCodePoints(int index, int codePointOffset) {
return super.offsetByCodePoints(index, codePointOffset);
}
@Override
public synchronized String toString() {
if (toStringCache == null) {
toStringCache = Arrays.copyOfRange(value, 0, count);
}
return new String(toStringCache, true);
}
StringBuilder类：
@Override
public StringBuilder append(Object obj) {
return append(String.valueOf(obj));
}
@Override
public StringBuilder append(String str) {
super.append(str);
return this;
}
public StringBuilder append(StringBuffer sb) {
super.append(sb);
return this;
}
@Override
public StringBuilder append(CharSequence s) {
super.append(s);
return this;
}
@Override
public StringBuilder append(CharSequence s, int start, int end) {
super.append(s, start, end);
return this;
}
@Override
public StringBuilder append(char[] str) {
super.append(str);
return this;
}
我们可以看到在StringBuffer中的方法只要是会改变数据的，或是数据改变会影响执行的结果的都加了synchronized进行同步，且StringBuffer内部维护一个toStringCache属性，主要是防止多次调用toString方法消耗时间，而StringBuilder没有。所以可以得出StringBuffer是线程安全的，StringBuilder不是
为了深入了解我们来看AbstractStringBuilder源码吧
import sun.misc.FloatingDecimal;
import java.util.Arrays;
/**
* 一个可变的字符序列。
* <p>
* 实现可修改的字符串。在任何时间点它都包含一些
* 特定的字符序列，但长度和内容
* 可以通过某些方法调用来更改序列。
* <p>
* 除非另有说明，否则将{@code null}参数传递给构造函数
* 或此类中的方法将导致{@link NullPointerException}
* 抛出。
*/
abstract class AbstractStringBuilder implements Appendable, CharSequence {
/**
* 该值用于字符存储。
*/
char[] value;
/**
* 计数使用的字符数。
*/
int count;
/**
* 这个无参数构造函数对于子类的序列化是必需的。
*/
AbstractStringBuilder() {
}
/**
* 创建指定容量的AbstractStringBuilder。
*/
AbstractStringBuilder(int capacity) {
value = new char[capacity];
}
/**
* 返回长度（字符数）。
*
* @return 当前字符序列的长度 由此对象表示
*/
@Override
public int length() {
return count;
}
/**
* 返回当前容量。容量是存储量
* 可用于新插入的字符，超出分配范围
* 会发生。
*/
public int capacity() {
return value.length;
}
/**
* 确保容量至少等于指定的最小值。
* 如果当前容量小于参数，那么新的内部
* 数组分配更大的容量。新的容量是
* 更大的：
* <ul>
* <li>{@code minimumCapacity}参数。
* <li>旧容量的两倍，再加上{@code 2}。
* </ul>
* 如果{@code minimumCapacity}参数是非正的，那么这个
* 方法不采取任何行动，只是返回。
* 请注意，对此对象的后续操作可以减少
* 实际容量低于此处要求的容量。
*/
public void ensureCapacity(int minimumCapacity) {
if (minimumCapacity > 0)
ensureCapacityInternal(minimumCapacity);
}
/**
* 对于{@code minimumCapacity}的正值，此方法
* 表现得像{@code ensureCapacity}，但它永远不会
* 同步。
* 如果{@code minimumCapacity}由于数字而为非正数
* 溢出，此方法抛出{@code OutOfMemoryError}。
*/
private void ensureCapacityInternal(int minimumCapacity) {
// overflow-conscious code
if (minimumCapacity - value.length > 0) {
value = Arrays.copyOf(value,
newCapacity(minimumCapacity));
}
}
/**
* 要分配的最大数组大小（除非必要）。
* 有些VM会在数组中保留一些标题字。
* 尝试分配更大的数组可能会导致
* OutOfMemoryError：请求的数组大小超过VM限制
*/
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
/**
* 返回至少与给定最小容量一样大的容量。
* 返回当前容量增加相同数量+ 2如果
* 那就够了。
* 不会返回大于{@code MAX_ARRAY_SIZE}的容量
* 除非给定的最小容量大于此值。
*/
private int newCapacity(int minCapacity) {
// 新的容量增加为当前数组容量的两倍再加上2
int newCapacity = (value.length << 1) + 2;
// 如果新的容量还是小于指定的最小容量，
// 那么最小容量直接赋值给新容量
if (newCapacity - minCapacity < 0) {
newCapacity = minCapacity;
}
// 如果当前容量已经有MAX_ARRAY_SIZE最大容量的一半了，
// 那么新容量就超过MAX_ARRAY_SIZE或是可能溢出为负数，
// 通过下面的三目运算，一旦出现上面的情况，
// 结果返回hugeCapacity(minCapacity)的值，
// 否则返回newCapacity
return (newCapacity <= 0 || MAX_ARRAY_SIZE - newCapacity < 0)
? hugeCapacity(minCapacity)
: newCapacity;
}
private int hugeCapacity(int minCapacity) {
// 这里可能会让人疑惑，为什么要判断
// Integer.MAX_VALUE - minCapacity < 0，
// 最大值减去minCapacity，怎么可能为负数呢，
// 这里就要说明一下计算机运算方式了
// 最大值：2147483647 二进制：01111111111111111111111111111111
// 其补码为：01111111111111111111111111111111
// (不懂补码，这里可以跳过，这是计算机组成原理的知识)
//
// 最小值：-2147483648 二进制：10000000000000000000000000000000(溢出的原因)
// 最小值：--2147483648 二进制：10000000000000000000000000000000(溢出的原因)
// 其补码为：10000000000000000000000000000000
// 如果这里用最大值减最小值，计算机用补码运算
// 则 01111111111111111111111111111111 + 10000000000000000000000000000000
// 结果：11111111111111111111111111111111
// 转换成原码： 10000000000000000000000000000001 真值：-1
// 最前面一位，计算机将其当做符号位，
// 但是在运算的时候直接参与了运算，造成溢出
if (Integer.MAX_VALUE - minCapacity < 0) { // overflow
throw new OutOfMemoryError();
}
return (minCapacity > MAX_ARRAY_SIZE)
? minCapacity : MAX_ARRAY_SIZE;
}
/**
* 尝试减少用于字符序列的存储空间。
* 如果缓冲区大于保持其当前序列所需的缓冲区
* 字符，然后可以调整大小以提高空间效率。
* 调用此方法可能（但不是必须）影响该值
* 通过后续调用{@link #capacity（）}方法返回。
*/
public void trimToSize() {
if (count < value.length) {
value = Arrays.copyOf(value, count);
}
}
/**
* 设置字符序列的长度。
* 序列更改为新的字符序列
* 其长度由参数指定。
*/
public void setLength(int newLength) {
// 传入参数小于零，抛出异常
if (newLength < 0)
throw new StringIndexOutOfBoundsException(newLength);
// 最终数组长度一定大于或等于newLength，如果newLength小于当前长度
// 的两倍加2，那么数组最终长度为value.length << 1 +2
// 具体参考newCapacity(minimumCapacity)
ensureCapacityInternal(newLength);
if (count < newLength) {
Arrays.fill(value, count, newLength, '\0');
}
count = newLength;
}
/**
* 返回指定索引处此序列中的{@code char}值。
*/
@Override
public char charAt(int index) {
if ((index < 0) || (index >= count))
throw new StringIndexOutOfBoundsException(index);
return value[index];
}
/**
* 返回指定的字符（Unicode代码点）
* 指数。索引引用{@code char}值
* （Unicode代码单位），范围从{@code 0}到
* {@link #length（）} {@ code - 1}。
*/
public int codePointAt(int index) {
if ((index < 0) || (index >= count)) {
throw new StringIndexOutOfBoundsException(index);
}
return Character.codePointAtImpl(value, index, count);
}
/**
* 返回指定之前的字符（Unicode代码点）
* 指数。索引引用{@code char}值
* （Unicode代码单位），范围从{@code 1}到{@link
* ＃长度（）}。
*/
public int codePointBefore(int index) {
int i = index - 1;
if ((i < 0) || (i >= count)) {
throw new StringIndexOutOfBoundsException(index);
}
return Character.codePointBeforeImpl(value, index, 0);
}
/**
* 返回指定文本中的Unicode代码点数
* 此序列的范围。文本范围从指定的开始
*/
public int codePointCount(int beginIndex, int endIndex) {
if (beginIndex < 0 || endIndex > count || beginIndex > endIndex) {
throw new IndexOutOfBoundsException();
}
return Character.codePointCountImpl(value, beginIndex, endIndex - beginIndex);
}
/**
* 返回此序列中偏离的索引
* 通过{@code codePointOffset}代码给出{@code index}
* 分。未提供的代理人在文本范围内给出
* {@code index}和{@code codePointOffset}算作
* 每个代码点。
*/
public int offsetByCodePoints(int index, int codePointOffset) {
if (index < 0 || index > count) {
throw new IndexOutOfBoundsException();
}
return Character.offsetByCodePointsImpl(value, 0, count,
index, codePointOffset);
}
/**
* 字符从此序列复制到
* 目标字符数组{@code dst}。第一个字符
* 被复制在索引{@code srcBegin};最后一个字符
* 被复制在索引{@code srcEnd-1}。总人数
* 要复制的字符是{@code srcEnd-srcBegin}。该
* 字符被复制到{@code dst}的子数组中
* 在索引{@code dstBegin}并以索引结束：
* {@ code
* dstbegin +（srcEnd-srcBegin） - 1
* }
*/
public void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) {
if (srcBegin < 0)
throw new StringIndexOutOfBoundsException(srcBegin);
if ((srcEnd < 0) || (srcEnd > count))
throw new StringIndexOutOfBoundsException(srcEnd);
if (srcBegin > srcEnd)
throw new StringIndexOutOfBoundsException("srcBegin > srcEnd");
System.arraycopy(value, srcBegin, dst, dstBegin, srcEnd - srcBegin);
}
/**
* 指定索引处的字符设置为{@code ch}。这个
* 序列被改变以表示新的字符序列
* 与旧字符序列相同，只是它包含
* 位置{@code index}的字符{@code ch}。
* index参数必须大于或等于
* {@code 0}，小于此序列的长度。
*/
public void setCharAt(int index, char ch) {
if ((index < 0) || (index >= count))
throw new StringIndexOutOfBoundsException(index);
value[index] = ch;
}
/**
* 添加{@code Object}参数的字符串表示形式。
*/
public AbstractStringBuilder append(Object obj) {
return append(String.valueOf(obj));
}
/**
* 将指定的字符串追加到此字符序列。
* {@code String}参数的字符将被追加到
* 顺序，增加这个序列的长度的长度
* 论点。如果{@code str}是{@code null}，那么这四个
* 附加*字符{@code“null”}。
* <p>
* 方法的返回值是对象本身，则可以进行链式调用
*/
public AbstractStringBuilder append(String str) {
if (str == null)
// 为空字符串则添加字符串"null"
return appendNull();
// 获取字符串的长度
int len = str.length();
// 确保内部容量可以容纳count+len
ensureCapacityInternal(count + len);
// 将数据加入到value中
str.getChars(0, len, value, count);
count += len;
return this;
}
// 与添加字符串类似，不再累述
public AbstractStringBuilder append(StringBuffer sb) {
if (sb == null)
return appendNull();
int len = sb.length();
ensureCapacityInternal(count + len);
sb.getChars(0, len, value, count);
count += len;
return this;
}
/**
* @since 1.8
* 与添加字符串类似，不再累述
*/
AbstractStringBuilder append(AbstractStringBuilder asb) {
if (asb == null)
return appendNull();
int len = asb.length();
ensureCapacityInternal(count + len);
asb.getChars(0, len, value, count);
count += len;
return this;
}
//与添加字符串类似，不再累述
@Override
public AbstractStringBuilder append(CharSequence s) {
if (s == null)
return appendNull();
if (s instanceof String)
return this.append((String) s);
if (s instanceof AbstractStringBuilder)
return this.append((AbstractStringBuilder) s);
return this.append(s, 0, s.length());
}
// 添加null，会在value中添加字符串"null"
private AbstractStringBuilder appendNull() {
int c = count;
ensureCapacityInternal(c + 4);
final char[] value = this.value;
value[c++] = 'n';
value[c++] = 'u';
value[c++] = 'l';
value[c++] = 'l';
count = c;
return this;
}
/**
* Appends a subsequence of the specified {@code CharSequence} to this
* sequence.
* <p>
* Characters of the argument {@code s}, starting at
* index {@code start}, are appended, in order, to the contents of
* this sequence up to the (exclusive) index {@code end}. The length
* of this sequence is increased by the value of {@code end - start}.
* <p>
* Let <i>n</i> be the length of this character sequence just prior to
* execution of the {@code append} method. Then the character at
* index <i>k</i> in this character sequence becomes equal to the
* character at index <i>k</i> in this sequence, if <i>k</i> is less than
* <i>n</i>; otherwise, it is equal to the character at index
* <i>k+start-n</i> in the argument {@code s}.
* <p>
* If {@code s} is {@code null}, then this method appends
* characters as if the s parameter was a sequence containing the four
* characters {@code "null"}.
*
* @param s the sequence to append.
* @param start the starting index of the subsequence to be appended.
* @param end the end index of the subsequence to be appended.
* @return a reference to this object.
* @throws IndexOutOfBoundsException if
* {@code start} is negative, or
* {@code start} is greater than {@code end} or
* {@code end} is greater than {@code s.length()}
*/
@Override
public AbstractStringBuilder append(CharSequence s, int start, int end) {
if (s == null)
s = "null";
if ((start < 0) || (start > end) || (end > s.length()))
throw new IndexOutOfBoundsException(
"start " + start + ", end " + end + ", s.length() "
+ s.length());
int len = end - start;
ensureCapacityInternal(count + len);
for (int i = start, j = count; i < end; i++, j++)
value[j] = s.charAt(i);
count += len;
return this;
}
/**
* Appends the string representation of the {@code char} array
* argument to this sequence.
* <p>
* The characters of the array argument are appended, in order, to
* the contents of this sequence. The length of this sequence
* increases by the length of the argument.
* <p>
* The overall effect is exactly as if the argument were converted
* to a string by the method {@link String#valueOf(char[])},
* and the characters of that string were then
* {@link #append(String) appended} to this character sequence.
*
* @param str the characters to be appended.
* @return a reference to this object.
*/
public AbstractStringBuilder append(char[] str) {
int len = str.length;
ensureCapacityInternal(count + len);
System.arraycopy(str, 0, value, count, len);
count += len;
return this;
}
/**
* Appends the string representation of a subarray of the
* {@code char} array argument to this sequence.
* <p>
* Characters of the {@code char} array {@code str}, starting at
* index {@code offset}, are appended, in order, to the contents
* of this sequence. The length of this sequence increases
* by the value of {@code len}.
* <p>
* The overall effect is exactly as if the arguments were converted
* to a string by the method {@link String#valueOf(char[], int, int)},
* and the characters of that string were then
* {@link #append(String) appended} to this character sequence.
*
* @param str the characters to be appended.
* @param offset the index of the first {@code char} to append.
* @param len the number of {@code char}s to append.
* @return a reference to this object.
* @throws IndexOutOfBoundsException if {@code offset < 0} or {@code len < 0}
* or {@code offset+len > str.length}
*/
public AbstractStringBuilder append(char str[], int offset, int len) {
if (len > 0) // let arraycopy report AIOOBE for len < 0
ensureCapacityInternal(count + len);
System.arraycopy(str, offset, value, count, len);
count += len;
return this;
}
/**
* Appends the string representation of the {@code boolean}
* argument to the sequence.
* <p>
* The overall effect is exactly as if the argument were converted
* to a string by the method {@link String#valueOf(boolean)},
* and the characters of that string were then
* {@link #append(String) appended} to this character sequence.
*
* @param b a {@code boolean}.
* @return a reference to this object.
*/
public AbstractStringBuilder append(boolean b) {
if (b) {
ensureCapacityInternal(count + 4);
value[count++] = 't';
value[count++] = 'r';
value[count++] = 'u';
value[count++] = 'e';
} else {
ensureCapacityInternal(count + 5);
value[count++] = 'f';
value[count++] = 'a';
value[count++] = 'l';
value[count++] = 's';
value[count++] = 'e';
}
return this;
}
/**
* Appends the string representation of the {@code char}
* argument to this sequence.
* <p>
* The argument is appended to the contents of this sequence.
* The length of this sequence increases by {@code 1}.
* <p>
* The overall effect is exactly as if the argument were converted
* to a string by the method {@link String#valueOf(char)},
* and the character in that string were then
* {@link #append(String) appended} to this character sequence.
*
* @param c a {@code char}.
* @return a reference to this object.
*/
@Override
public AbstractStringBuilder append(char c) {
ensureCapacityInternal(count + 1);
value[count++] = c;
return this;
}
/**
* Appends the string representation of the {@code int}
* argument to this sequence.
* <p>
* The overall effect is exactly as if the argument were converted
* to a string by the method {@link String#valueOf(int)},
* and the characters of that string were then
* {@link #append(String) appended} to this character sequence.
*
* @param i an {@code int}.
* @return a reference to this object.
*/
public AbstractStringBuilder append(int i) {
if (i == Integer.MIN_VALUE) {
append("-2147483648");
return this;
}
int appendedLength = (i < 0) ? Integer.stringSize(-i) + 1
: Integer.stringSize(i);
int spaceNeeded = count + appendedLength;
ensureCapacityInternal(spaceNeeded);
Integer.getChars(i, spaceNeeded, value);
count = spaceNeeded;
return this;
}
/**
* Appends the string representation of the {@code long}
* argument to this sequence.
* <p>
* The overall effect is exactly as if the argument were converted
* to a string by the method {@link String#valueOf(long)},
* and the characters of that string were then
* {@link #append(String) appended} to this character sequence.
*
* @param l a {@code long}.
* @return a reference to this object.
*/
public AbstractStringBuilder append(long l) {
if (l == Long.MIN_VALUE) {
append("-9223372036854775808");
return this;
}
int appendedLength = (l < 0) ? Long.stringSize(-l) + 1
: Long.stringSize(l);
int spaceNeeded = count + appendedLength;
ensureCapacityInternal(spaceNeeded);
Long.getChars(l, spaceNeeded, value);
count = spaceNeeded;
return this;
}
/**
* Appends the string representation of the {@code float}
* argument to this sequence.
* <p>
* The overall effect is exactly as if the argument were converted
* to a string by the method {@link String#valueOf(float)},
* and the characters of that string were then
* {@link #append(String) appended} to this character sequence.
*
* @param f a {@code float}.
* @return a reference to this object.
*/
public AbstractStringBuilder append(float f) {
FloatingDecimal.appendTo(f, this);
return this;
}
/**
* Appends the string representation of the {@code double}
* argument to this sequence.
* <p>
* The overall effect is exactly as if the argument were converted
* to a string by the method {@link String#valueOf(double)},
* and the characters of that string were then
* {@link #append(String) appended} to this character sequence.
*
* @param d a {@code double}.
* @return a reference to this object.
*/
public AbstractStringBuilder append(double d) {
FloatingDecimal.appendTo(d, this);
return this;
}
/**
* 删除此序列的子字符串中的字符。
* 子字符串从指定的{@code start}开始并延伸到
* 索引{@code end - 1}或结尾处的字符
* 序列如果不存在这样的字符。如果
* {@code start}等于{@code end}，不做任何更改。
*
* @param start The beginning index, inclusive.
* @param end The ending index, exclusive.
* @return This object.
* @throws StringIndexOutOfBoundsException if {@code start}
* is negative, greater than {@code length()}, or
* greater than {@code end}.
*/
public AbstractStringBuilder delete(int start, int end) {
if (start < 0)
throw new StringIndexOutOfBoundsException(start);
if (end > count)
end = count;
if (start > end)
throw new StringIndexOutOfBoundsException();
int len = end - start;
if (len > 0) {
// 通过这个静态方法将value中的值进行移动，底层用C实现，很快
System.arraycopy(value, start + len, value, start, count - end);
count -= len;
}
return this;
}
/**
* Appends the string representation of the {@code codePoint}
* argument to this sequence.
*
* <p> The argument is appended to the contents of this sequence.
* The length of this sequence increases by
* {@link Character#charCount(int) Character.charCount(codePoint)}.
*
* <p> The overall effect is exactly as if the argument were
* converted to a {@code char} array by the method
* {@link Character#toChars(int)} and the character in that array
* were then {@link #append(char[]) appended} to this character
* sequence.
*
* @param codePoint a Unicode code point
* @return a reference to this object.
* @throws IllegalArgumentException if the specified
* {@code codePoint} isn't a valid Unicode code point
*/
public AbstractStringBuilder appendCodePoint(int codePoint) {
final int count = this.count;
if (Character.isBmpCodePoint(codePoint)) {
ensureCapacityInternal(count + 1);
value[count] = (char) codePoint;
this.count = count + 1;
} else if (Character.isValidCodePoint(codePoint)) {
ensureCapacityInternal(count + 2);
Character.toSurrogates(codePoint, value, count);
this.count = count + 2;
} else {
throw new IllegalArgumentException();
}
return this;
}
/**
* Removes the {@code char} at the specified position in this
* sequence. This sequence is shortened by one {@code char}.
*
* <p>Note: If the character at the given index is a supplementary
* character, this method does not remove the entire character. If
* correct handling of supplementary characters is required,
* determine the number of {@code char}s to remove by calling
* {@code Character.charCount(thisSequence.codePointAt(index))},
* where {@code thisSequence} is this sequence.
*
* @param index Index of {@code char} to remove
* @return This object.
* @throws StringIndexOutOfBoundsException if the {@code index}
* is negative or greater than or equal to
* {@code length()}.
*/
public AbstractStringBuilder deleteCharAt(int index) {
if ((index < 0) || (index >= count))
throw new StringIndexOutOfBoundsException(index);
System.arraycopy(value, index + 1, value, index, count - index - 1);
count--;
return this;
}
/**
* Replaces the characters in a substring of this sequence
* with characters in the specified {@code String}. The substring
* begins at the specified {@code start} and extends to the character
* at index {@code end - 1} or to the end of the
* sequence if no such character exists. First the
* characters in the substring are removed and then the specified
* {@code String} is inserted at {@code start}. (This
* sequence will be lengthened to accommodate the
* specified String if necessary.)
*
* @param start The beginning index, inclusive.
* @param end The ending index, exclusive.
* @param str String that will replace previous contents.
* @return This object.
* @throws StringIndexOutOfBoundsException if {@code start}
* is negative, greater than {@code length()}, or
* greater than {@code end}.
*/
public AbstractStringBuilder replace(int start, int end, String str) {
if (start < 0)
throw new StringIndexOutOfBoundsException(start);
if (start > count)
throw new StringIndexOutOfBoundsException("start > length()");
if (start > end)
throw new StringIndexOutOfBoundsException("start > end");
if (end > count)
end = count;
int len = str.length();
int newCount = count + len - (end - start);
ensureCapacityInternal(newCount);
System.arraycopy(value, end, value, start + len, count - end);
str.getChars(value, start);
count = newCount;
return this;
}
/**
* Returns a new {@code String} that contains a subsequence of
* characters currently contained in this character sequence. The
* substring begins at the specified index and extends to the end of
* this sequence.
*
* @param start The beginning index, inclusive.
* @return The new string.
* @throws StringIndexOutOfBoundsException if {@code start} is
* less than zero, or greater than the length of this object.
*/
public String substring(int start) {
return substring(start, count);
}
/**
* Returns a new character sequence that is a subsequence of this sequence.
*
* <p> An invocation of this method of the form
*
* <pre>{@code
* sb.subSequence(begin, end)}</pre>
* <p>
* behaves in exactly the same way as the invocation
*
* <pre>{@code
* sb.substring(begin, end)}</pre>
* <p>
* This method is provided so that this class can
* implement the {@link CharSequence} interface.
*
* @param start the start index, inclusive.
* @param end the end index, exclusive.
* @return the specified subsequence.
* @throws IndexOutOfBoundsException if {@code start} or {@code end} are negative,
* if {@code end} is greater than {@code length()},
* or if {@code start} is greater than {@code end}
* @spec JSR-51
*/
@Override
public CharSequence subSequence(int start, int end) {
return substring(start, end);
}
/**
* 返回包含子序列的新{@code String}
* 此序列中当前包含的字符。该
* substring从指定的{@code start}开始
* 扩展到索引{@code end - 1}处的字符。
*
* @param start The beginning index, inclusive.
* @param end The ending index, exclusive.
* @return The new string.
* @throws StringIndexOutOfBoundsException if {@code start}
* or {@code end} are negative or greater than
* {@code length()}, or {@code start} is
* greater than {@code end}.
*/
public String substring(int start, int end) {
if (start < 0)
throw new StringIndexOutOfBoundsException(start);
if (end > count)
throw new StringIndexOutOfBoundsException(end);
if (start > end)
throw new StringIndexOutOfBoundsException(end - start);
return new String(value, start, end - start);
}
/**
* 插入{@code str}子数组的字符串表示形式
* 数组参数进入此序列。子阵列始于
* 指定{@code offset}并扩展{@code len} {@code char}。
* 子阵列的字符插入到此序列中
* {@code index}指示的位置。这个的长度
* 序列增加{@code len} {@code char}。
*
* @param index position at which to insert subarray.
* @param str A {@code char} array.
* @param offset the index of the first {@code char} in subarray to
* be inserted.
* @param len the number of {@code char}s in the subarray to
* be inserted.
* @return This object
* @throws StringIndexOutOfBoundsException if {@code index}
* is negative or greater than {@code length()}, or
* {@code offset} or {@code len} are negative, or
* {@code (offset+len)} is greater than
* {@code str.length}.
*/
public AbstractStringBuilder insert(int index, char[] str, int offset,
int len) {
if ((index < 0) || (index > length()))
throw new StringIndexOutOfBoundsException(index);
if ((offset < 0) || (len < 0) || (offset > str.length - len))
throw new StringIndexOutOfBoundsException(
"offset " + offset + ", len " + len + ", str.length "
+ str.length);
ensureCapacityInternal(count + len);
System.arraycopy(value, index, value, index + len, count - index);
System.arraycopy(str, offset, value, index, len);
count += len;
return this;
}
/**
* Inserts the string representation of the {@code Object}
* argument into this character sequence.
* <p>
* The overall effect is exactly as if the second argument were
* converted to a string by the method {@link String#valueOf(Object)},
* and the characters of that string were then
* {@link #insert(int, String) inserted} into this character
* sequence at the indicated offset.
* <p>
* The {@code offset} argument must be greater than or equal to
* {@code 0}, and less than or equal to the {@linkplain #length() length}
* of this sequence.
*
* @param offset the offset.
* @param obj an {@code Object}.
* @return a reference to this object.
* @throws StringIndexOutOfBoundsException if the offset is invalid.
*/
public AbstractStringBuilder insert(int offset, Object obj) {
return insert(offset, String.valueOf(obj));
}
/**
* Inserts the string into this character sequence.
* <p>
* The characters of the {@code String} argument are inserted, in
* order, into this sequence at the indicated offset, moving up any
* characters originally above that position and increasing the length
* of this sequence by the length of the argument. If
* {@code str} is {@code null}, then the four characters
* {@code "null"} are inserted into this sequence.
* <p>
* The character at index <i>k</i> in the new character sequence is
* equal to:
* <ul>
* <li>the character at index <i>k</i> in the old character sequence, if
* <i>k</i> is less than {@code offset}
* <li>the character at index <i>k</i>{@code -offset} in the
* argument {@code str}, if <i>k</i> is not less than
* {@code offset} but is less than {@code offset+str.length()}
* <li>the character at index <i>k</i>{@code -str.length()} in the
* old character sequence, if <i>k</i> is not less than
* {@code offset+str.length()}
* </ul><p>
* The {@code offset} argument must be greater than or equal to
* {@code 0}, and less than or equal to the {@linkplain #length() length}
* of this sequence.
*
* @param offset the offset.
* @param str a string.
* @return a reference to this object.
* @throws StringIndexOutOfBoundsException if the offset is invalid.
*/
public AbstractStringBuilder insert(int offset, String str) {
if ((offset < 0) || (offset > length()))
throw new StringIndexOutOfBoundsException(offset);
if (str == null)
str = "null";
int len = str.length();
ensureCapacityInternal(count + len);
System.arraycopy(value, offset, value, offset + len, count - offset);
str.getChars(value, offset);
count += len;
return this;
}
/**
* Inserts the string representation of the {@code char} array
* argument into this sequence.
* <p>
* The characters of the array argument are inserted into the
* contents of this sequence at the position indicated by
* {@code offset}. The length of this sequence increases by
* the length of the argument.
* <p>
* The overall effect is exactly as if the second argument were
* converted to a string by the method {@link String#valueOf(char[])},
* and the characters of that string were then
* {@link #insert(int, String) inserted} into this character
* sequence at the indicated offset.
* <p>
* The {@code offset} argument must be greater than or equal to
* {@code 0}, and less than or equal to the {@linkplain #length() length}
* of this sequence.
*
* @param offset the offset.
* @param str a character array.
* @return a reference to this object.
* @throws StringIndexOutOfBoundsException if the offset is invalid.
*/
public AbstractStringBuilder insert(int offset, char[] str) {
if ((offset < 0) || (offset > length()))
throw new StringIndexOutOfBoundsException(offset);
int len = str.length;
ensureCapacityInternal(count + len);
System.arraycopy(value, offset, value, offset + len, count - offset);
System.arraycopy(str, 0, value, offset, len);
count += len;
return this;
}
/**
* Inserts the specified {@code CharSequence} into this sequence.
* <p>
* The characters of the {@code CharSequence} argument are inserted,
* in order, into this sequence at the indicated offset, moving up
* any characters originally above that position and increasing the length
* of this sequence by the length of the argument s.
* <p>
* The result of this method is exactly the same as if it were an
* invocation of this object's
* {@link #insert(int, CharSequence, int, int) insert}(dstOffset, s, 0, s.length())
* method.
*
* <p>If {@code s} is {@code null}, then the four characters
* {@code "null"} are inserted into this sequence.
*
* @param dstOffset the offset.
* @param s the sequence to be inserted
* @return a reference to this object.
* @throws IndexOutOfBoundsException if the offset is invalid.
*/
public AbstractStringBuilder insert(int dstOffset, CharSequence s) {
if (s == null)
s = "null";
if (s instanceof String)
return this.insert(dstOffset, (String) s);
return this.insert(dstOffset, s, 0, s.length());
}
/**
* Inserts a subsequence of the specified {@code CharSequence} into
* this sequence.
* <p>
* The subsequence of the argument {@code s} specified by
* {@code start} and {@code end} are inserted,
* in order, into this sequence at the specified destination offset, moving
* up any characters originally above that position. The length of this
* sequence is increased by {@code end - start}.
* <p>
* The character at index <i>k</i> in this sequence becomes equal to:
* <ul>
* <li>the character at index <i>k</i> in this sequence, if
* <i>k</i> is less than {@code dstOffset}
* <li>the character at index <i>k</i>{@code +start-dstOffset} in
* the argument {@code s}, if <i>k</i> is greater than or equal to
* {@code dstOffset} but is less than {@code dstOffset+end-start}
* <li>the character at index <i>k</i>{@code -(end-start)} in this
* sequence, if <i>k</i> is greater than or equal to
* {@code dstOffset+end-start}
* </ul><p>
* The {@code dstOffset} argument must be greater than or equal to
* {@code 0}, and less than or equal to the {@linkplain #length() length}
* of this sequence.
* <p>The start argument must be nonnegative, and not greater than
* {@code end}.
* <p>The end argument must be greater than or equal to
* {@code start}, and less than or equal to the length of s.
*
* <p>If {@code s} is {@code null}, then this method inserts
* characters as if the s parameter was a sequence containing the four
* characters {@code "null"}.
*
* @param dstOffset the offset in this sequence.
* @param s the sequence to be inserted.
* @param start the starting index of the subsequence to be inserted.
* @param end the end index of the subsequence to be inserted.
* @return a reference to this object.
* @throws IndexOutOfBoundsException if {@code dstOffset}
* is negative or greater than {@code this.length()}, or
* {@code start} or {@code end} are negative, or
* {@code start} is greater than {@code end} or
* {@code end} is greater than {@code s.length()}
*/
public AbstractStringBuilder insert(int dstOffset, CharSequence s,
int start, int end) {
if (s == null)
s = "null";
if ((dstOffset < 0) || (dstOffset > this.length()))
throw new IndexOutOfBoundsException("dstOffset " + dstOffset);
if ((start < 0) || (end < 0) || (start > end) || (end > s.length()))
throw new IndexOutOfBoundsException(
"start " + start + ", end " + end + ", s.length() "
+ s.length());
int len = end - start;
ensureCapacityInternal(count + len);
System.arraycopy(value, dstOffset, value, dstOffset + len,
count - dstOffset);
for (int i = start; i < end; i++)
value[dstOffset++] = s.charAt(i);
count += len;
return this;
}
/**
* Inserts the string representation of the {@code boolean}
* argument into this sequence.
* <p>
* The overall effect is exactly as if the second argument were
* converted to a string by the method {@link String#valueOf(boolean)},
* and the characters of that string were then
* {@link #insert(int, String) inserted} into this character
* sequence at the indicated offset.
* <p>
* The {@code offset} argument must be greater than or equal to
* {@code 0}, and less than or equal to the {@linkplain #length() length}
* of this sequence.
*
* @param offset the offset.
* @param b a {@code boolean}.
* @return a reference to this object.
* @throws StringIndexOutOfBoundsException if the offset is invalid.
*/
public AbstractStringBuilder insert(int offset, boolean b) {
return insert(offset, String.valueOf(b));
}
/**
* Inserts the string representation of the {@code char}
* argument into this sequence.
* <p>
* The overall effect is exactly as if the second argument were
* converted to a string by the method {@link String#valueOf(char)},
* and the character in that string were then
* {@link #insert(int, String) inserted} into this character
* sequence at the indicated offset.
* <p>
* The {@code offset} argument must be greater than or equal to
* {@code 0}, and less than or equal to the {@linkplain #length() length}
* of this sequence.
*
* @param offset the offset.
* @param c a {@code char}.
* @return a reference to this object.
* @throws IndexOutOfBoundsException if the offset is invalid.
*/
public AbstractStringBuilder insert(int offset, char c) {
ensureCapacityInternal(count + 1);
System.arraycopy(value, offset, value, offset + 1, count - offset);
value[offset] = c;
count += 1;
return this;
}
/**
* Inserts the string representation of the second {@code int}
* argument into this sequence.
* <p>
* The overall effect is exactly as if the second argument were
* converted to a string by the method {@link String#valueOf(int)},
* and the characters of that string were then
* {@link #insert(int, String) inserted} into this character
* sequence at the indicated offset.
* <p>
* The {@code offset} argument must be greater than or equal to
* {@code 0}, and less than or equal to the {@linkplain #length() length}
* of this sequence.
*
* @param offset the offset.
* @param i an {@code int}.
* @return a reference to this object.
* @throws StringIndexOutOfBoundsException if the offset is invalid.
*/
public AbstractStringBuilder insert(int offset, int i) {
return insert(offset, String.valueOf(i));
}
/**
* Inserts the string representation of the {@code long}
* argument into this sequence.
* <p>
* The overall effect is exactly as if the second argument were
* converted to a string by the method {@link String#valueOf(long)},
* and the characters of that string were then
* {@link #insert(int, String) inserted} into this character
* sequence at the indicated offset.
* <p>
* The {@code offset} argument must be greater than or equal to
* {@code 0}, and less than or equal to the {@linkplain #length() length}
* of this sequence.
*
* @param offset the offset.
* @param l a {@code long}.
* @return a reference to this object.
* @throws StringIndexOutOfBoundsException if the offset is invalid.
*/
public AbstractStringBuilder insert(int offset, long l) {
return insert(offset, String.valueOf(l));
}
/**
* Inserts the string representation of the {@code float}
* argument into this sequence.
* <p>
* The overall effect is exactly as if the second argument were
* converted to a string by the method {@link String#valueOf(float)},
* and the characters of that string were then
* {@link #insert(int, String) inserted} into this character
* sequence at the indicated offset.
* <p>
* The {@code offset} argument must be greater than or equal to
* {@code 0}, and less than or equal to the {@linkplain #length() length}
* of this sequence.
*
* @param offset the offset.
* @param f a {@code float}.
* @return a reference to this object.
* @throws StringIndexOutOfBoundsException if the offset is invalid.
*/
public AbstractStringBuilder insert(int offset, float f) {
return insert(offset, String.valueOf(f));
}
/**
* Inserts the string representation of the {@code double}
* argument into this sequence.
* <p>
* The overall effect is exactly as if the second argument were
* converted to a string by the method {@link String#valueOf(double)},
* and the characters of that string were then
* {@link #insert(int, String) inserted} into this character
* sequence at the indicated offset.
* <p>
* The {@code offset} argument must be greater than or equal to
* {@code 0}, and less than or equal to the {@linkplain #length() length}
* of this sequence.
*
* @param offset the offset.
* @param d a {@code double}.
* @return a reference to this object.
* @throws StringIndexOutOfBoundsException if the offset is invalid.
*/
public AbstractStringBuilder insert(int offset, double d) {
return insert(offset, String.valueOf(d));
}
/**
* Returns the index within this string of the first occurrence of the
* specified substring. The integer returned is the smallest value
* <i>k</i> such that:
* <pre>{@code
* this.toString().startsWith(str, <i>k</i>)
* }</pre>
* is {@code true}.
*
* @param str any string.
* @return if the string argument occurs as a substring within this
* object, then the index of the first character of the first
* such substring is returned; if it does not occur as a
* substring, {@code -1} is returned.
*/
public int indexOf(String str) {
return indexOf(str, 0);
}
/**
* 返回第一次出现的字符串中的索引
* 指定的子字符串，从指定的索引开始。整数
* 返回的是{@code k}的最小值，其中：
* <pre>{@code
* k >= Math.min(fromIndex, this.length()) &&
* this.toString().startsWith(str, k)
* }</pre>
* If no such value of <i>k</i> exists, then -1 is returned.
*
* @param str the substring for which to search.
* @param fromIndex the index from which to start the search.
* @return the index within this string of the first occurrence of the
* specified substring, starting at the specified index.
*/
public int indexOf(String str, int fromIndex) {
return String.indexOf(value, 0, count, str, fromIndex);
}
/**
* Returns the index within this string of the rightmost occurrence
* of the specified substring. The rightmost empty string "" is
* considered to occur at the index value {@code this.length()}.
* The returned index is the largest value <i>k</i> such that
* <pre>{@code
* this.toString().startsWith(str, k)
* }</pre>
* is true.
*
* @param str the substring to search for.
* @return if the string argument occurs one or more times as a substring
* within this object, then the index of the first character of
* the last such substring is returned. If it does not occur as
* a substring, {@code -1} is returned.
*/
public int lastIndexOf(String str) {
return lastIndexOf(str, count);
}
/**
* Returns the index within this string of the last occurrence of the
* specified substring. The integer returned is the largest value <i>k</i>
* such that:
* <pre>{@code
* k <= Math.min(fromIndex, this.length()) &&
* this.toString().startsWith(str, k)
* }</pre>
* If no such value of <i>k</i> exists, then -1 is returned.
*
* @param str the substring to search for.
* @param fromIndex the index to start the search from.
* @return the index within this sequence of the last occurrence of the
* specified substring.
*/
public int lastIndexOf(String str, int fromIndex) {
return String.lastIndexOf(value, 0, count, str, fromIndex);
}
/**
* 该方法用于将字符序列反转，如"我爱你"执行reverse后变成"你爱我"。
* 1.hasSurrogates用来标识字符序列中是否包含`surrogates pair`
* <p>
* `surrogates pair`
* UTF-16中用于扩展字符而使用的编码方式，是一种采用四个字节(两个UTF-16编码)来表示一个字符。
* char在java中是16位的，刚好是一个UTF-16编码。而字符串中可能含有Surrogate Pair,
* 但他们是一个单一完整的字符，只不过是用两个char来表示而已，
* 因此在反转字符串的过程中Surrogate Pairs 是不应该被反转的。
* 而reverseAllValidSurrogatePairs方法就是对Surrogate Pair进行处理。
*/
public AbstractStringBuilder reverse() {
boolean hasSurrogates = false;
int n = count - 1;
// j的初始值就是中间一个数的左边的数下标
for (int j = (n - 1) >> 1; j >= 0; j--) {
int k = n - j;
char cj = value[j];
char ck = value[k];
value[j] = ck;
value[k] = cj;
// 判断是否有`surrogates pair`
if (Character.isSurrogate(cj) ||
Character.isSurrogate(ck)) {
hasSurrogates = true;
}
}
// 如果有surrogates pair`的话，执行reverseAllValidSurrogatePairs
if (hasSurrogates) {
reverseAllValidSurrogatePairs();
}
return this;
}
/**
* 用于reverse（）的概述辅助方法
* 主要将`surrogates pair`重新互换回来
*/
private void reverseAllValidSurrogatePairs() {
for (int i = 0; i < count - 1; i++) {
char c2 = value[i];
if (Character.isLowSurrogate(c2)) {
char c1 = value[i + 1];
if (Character.isHighSurrogate(c1)) {
value[i++] = c1;
value[i] = c2;
}
}
}
}
/**
* Returns a string representing the data in this sequence.
* A new {@code String} object is allocated and initialized to
* contain the character sequence currently represented by this
* object. This {@code String} is then returned. Subsequent
* changes to this sequence do not affect the contents of the
* {@code String}.
*
* @return a string representation of this sequence of characters.
*/
@Override
public abstract String toString();
/**
* {@code String}需要contentEquals方法。
*/
final char[] getValue() {
return value;
}
}
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