JDK源码解析<三> java.lang.AbstractStr

作者: 小吖么小一郎 | 来源:发表于2019-07-08 15:05 被阅读0次

可变性

AbstractStringBuilder中变量：char value[]; int count; 都不是final修饰的，并且也定义了getValues方法让我们可以直接拿到value[],value实际上是个动态数组。

方法

public int length(): 返回已经存储的实际长度（就是count值）
public int capacity(): capacity是’容量’的意思,得到目前该value数组的实际大小
ensureCapacity(int minimumCapacity): 确保value数组的容量是否够用，如果不够用，调用expandCapacity(minimumCapacity)方法扩容，参数为需要的容量

 public void ensureCapacity(int minimumCapacity) {
    if (minimumCapacity > value.length) {
        expandCapacity(minimumCapacity);
    }
  }

expandCapacity(int minimumCapacity):对数组进行扩容，参数为需要的容量

 void expandCapacity(int minimumCapacity) {
    int newCapacity = (value.length + 1) * 2;
        if (newCapacity < 0) {
            newCapacity = Integer.MAX_VALUE;
        } else if (minimumCapacity > newCapacity) {
        newCapacity = minimumCapacity;
    }
        value = Arrays.copyOf(value, newCapacity);
}

扩容的算法： 
如果调用了该函数，说明容量不够用了，先将当前容量+1的二倍(newCapacity)与需要的容量(minimumCapacity)比较。 
如果比需要的容量大，那就将容量扩大到容量+1的二倍；如果比需要的容量小，那就直接扩大到需要的容量。 
使用Arrays.copyOf()这个非常熟悉的方法来使数组容量动态扩大

public void trimToSize(): 如果value数组的容量有多余的，那么就把多余的全部都释放掉
setLength(int newLength):强制增大实际长度count的大小，容量如果不够就用 expandCapacity()扩大；将扩大的部分全部用’\0’（ASCII码中的null）来初始化

 public void setLength(int newLength) {
    if (newLength < 0)  throw new StringIndexOutOfBoundsException(newLength);
    if (newLength > value.length)  expandCapacity(newLength);
    if (count < newLength) {
        for (; count < newLength; count++)
        value[count] = '\0';
    } else {
            count = newLength;
        }
}

public char charAt(int index): 得到下标为index的字符
public int codePointAt(int index): 得到代码点
public void getChars(int srcBegin, int srcEnd, char dst[],int dstBegin): 将value[]的[srcBegin, srcEnd)拷贝到dst[]数组的desBegin开始处
public String substring(int start) / public String substring(int start, int end) 得到子字符串
public CharSequence subSequence(int start, int end): 得到一个子字符序列
reverse():将value给倒序存放（注意改变的就是本value，而不是创建了一个新的AbstractStringBuilder然后value为倒序）

public AbstractStringBuilder reverse() {
    boolean hasSurrogate = false;
    int n = count - 1;
    for (int j = (n-1) >> 1; j >= 0; --j) {
        char temp = value[j];
        char temp2 = value[n - j];
        if (!hasSurrogate) {
        hasSurrogate = (temp >= Character.MIN_SURROGATE && temp <= Character.MAX_SURROGATE)
            || (temp2 >= Character.MIN_SURROGATE && temp2 <= Character.MAX_SURROGATE);
        }
        value[j] = temp2;
        value[n - j] = temp;
    }
    if (hasSurrogate) {
        // Reverse back all valid surrogate pairs
        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;
            }
        }
        }
    }
    return this;
}

public abstract String toString(); 唯一的一个抽象方法：toString()
public void setCharAt(int index, char ch): 直接设置下标为index的字符为ch
public AbstractStringBuilder replace(int start, int end, String str): 用字符串str替换掉value[]数组的[start,end)部分
append都表示’追加’，insert都表示’插入

// 利用Object（或任何对象）的toString方法转成字符串然后添加到该value[]中
public AbstractStringBuilder append(Object obj) {
   return append(String.valueOf(obj));
   }

// append(String str)/append(StringBuffer sb)/append(CharSequence s)。直接修改value[]，并且’添加’的意思为链接到原value[]的实际count的后面
// 同时注意返回的都是AbstractStringBuilder，意味着append方法可以连续无限调用，即AbstractStringBuilder对象.append(参数1).append(参数2).append(参数三)…………;
 public AbstractStringBuilder append(String str) {
    if (str == null) str = "null";
        int len = str.length();
    if (len == 0) return this;
    int newCount = count + len;
    if (newCount > value.length)
        expandCapacity(newCount);
    str.getChars(0, len, value, count);
    count = newCount;
    return this;
    }
    // Documentation in subclasses because of synchro difference
    public AbstractStringBuilder append(StringBuffer sb) {
    if (sb == null)
            return append("null");
    int len = sb.length();
    int newCount = count + len;
    if (newCount > value.length)
        expandCapacity(newCount);
    sb.getChars(0, len, value, count);
    count = newCount;
    return this;
    }
    // Documentation in subclasses because of synchro difference
    public AbstractStringBuilder append(CharSequence s) {
        if (s == null)
            s = "null";
        if (s instanceof String)
            return this.append((String)s);
        if (s instanceof StringBuffer)
            return this.append((StringBuffer)s);
        return this.append(s, 0, s.length());
    }

public AbstractStringBuilder append(CharSequence s, int start, int end):添加字符序列s的部分序列，范围是[start,end)
public AbstractStringBuilder append(char str[]):添加一个字符数组
public AbstractStringBuilder append(char str[], int offset, int len):添加一个字符数组的一部分，该部分的范围是[offset,offset+len);
public AbstractStringBuilder append(boolean b):添加布尔值。
public AbstractStringBuilder append(char c):添加一个字符
public AbstractStringBuilder append(int i):添加一个整数'
public AbstractStringBuilder append(long l):添加一个长整型的数据，原理同上一个append
public AbstractStringBuilder append(float f)/append(double d):添加一个浮点数。
(insert的核心代码)在value[]的下标为index位置插入数组str的一部分，该部分的范围为：[offset,offset+len);

 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);
    int newCount = count + len;
    if (newCount > value.length)
        expandCapacity(newCount);
    System.arraycopy(value, index, value, index + len, count - index);
    System.arraycopy(str, offset, value, index, len);
    count = newCount;
    return this;
}

// insert(int offset, Object obj)：在value[]的offset位置插入Object（或者说所有对象）的String版
public AbstractStringBuilder insert(int offset, Object obj) {
    return insert(offset, String.valueOf(obj));
}

// insert(int offset, String str):在value[]的offset位置插入字符串
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();
    int newCount = count + len;
    if (newCount > value.length)
        expandCapacity(newCount);
    System.arraycopy(value, offset, value, offset + len, count - offset);
    str.getChars(value, offset);
    count = newCount;
    return this;
}

//  insert(int offset, char str[]):在value[]的offset位置插入字符数组
public AbstractStringBuilder insert(int offset, char str[]) {
    if ((offset < 0) || (offset > length()))
        throw new StringIndexOutOfBoundsException(offset);
    int len = str.length;
    int newCount = count + len;
    if (newCount > value.length)
        expandCapacity(newCount);
    System.arraycopy(value, offset, value, offset + len, count - offset);
    System.arraycopy(str, 0, value, offset, len);
    count = newCount;
    return this;
}

//  insert(int dstOffset, CharSequence s)/insert(int dstOffset, CharSequence s,int start, int end):插入字符序列
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());
}
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;
        if (len == 0)
            return this;
    int newCount = count + len;
    if (newCount > value.length)
        expandCapacity(newCount);
    System.arraycopy(value, dstOffset, value, dstOffset + len,
                         count - dstOffset);
    for (int i=start; i<end; i++)
            value[dstOffset++] = s.charAt(i);
    count = newCount;
        return this;
}

// 插入基本类型：除了char是直接插入外，其他都是先转成String，然后调用编号为28的insert方法
public AbstractStringBuilder insert(int offset, boolean b) {
    return insert(offset, String.valueOf(b));
}
public AbstractStringBuilder insert(int offset, char c) {
    int newCount = count + 1;
    if (newCount > value.length)
        expandCapacity(newCount);
    System.arraycopy(value, offset, value, offset + 1, count - offset);
    value[offset] = c;
    count = newCount;
    return this;
}
public AbstractStringBuilder insert(int offset, int i) {
    return insert(offset, String.valueOf(i));
}
public AbstractStringBuilder insert(int offset, long l) {
    return insert(offset, String.valueOf(l));
}
public AbstractStringBuilder insert(int offset, float f) {
    return insert(offset, String.valueOf(f));
}
public AbstractStringBuilder insert(int offset, double d) {
    return insert(offset, String.valueOf(d));
}

delete

//  删掉value数组的[start,end)部分，并将end后面的数据移到start位置
 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) {
            System.arraycopy(value, start+len, value, start, count-end);
            count -= len;
        }
        return this;
}

//  删除下标为index的数据，并将后面的数据前移一位
 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;
}

query

//  在value[]中找字符串str，若能找到，返回第一个字符串的第一个字符的下标
 public int indexOf(String str) {
    return indexOf(str, 0);
}

//  从fromIndex开始，在value[]中找字符串str，若能找到，返回第一个字符串的第一个字符的下标
public int indexOf(String str, int fromIndex) {
        return String.indexOf(value, 0, count,
                              str.toCharArray(), 0, str.length(), fromIndex);
}

//  从后往前找
public int lastIndexOf(String str) {
        return lastIndexOf(str, count);
}

//  从后往前到fromIndex，找子串str
public int lastIndexOf(String str, int fromIndex) {
        return String.lastIndexOf(value, 0, count,
                              str.toCharArray(), 0, str.length(), fromIndex);
}

JDK源码解析<三> java.lang.AbstractStr

可变性

方法

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