基于Java8，更优雅的字符串操作

字符串创建

//1.String()
String str = new String();

//2.String(char[] a)
char[] a = {'a','b','c','d'};
String str = new String(a);

//3.String(char[] a, int offset, int length)
char[] a = {'a','b','c','d'}
String str = new String(a, 1, 2);

Java8中的字符串连接

Collectors.joining

在JDK8中，可以采用函数式编程（使用 Collectors.joining 收集器）的方式对字符串进行更优雅的连接。

Collectors.joining 收集器 支持灵活的参数配置，可以指定字符串连接时的 分隔符，前缀 和 后缀 字符串。

// 定义人名数组
final String[] names = {"Zebe", "Hebe", "Mary", "July", "David"};
Stream<String> stream1 = Stream.of(names);
Stream<String> stream2 = Stream.of(names);
Stream<String> stream3 = Stream.of(names);
// 拼接成 [x, y, z] 形式
String result1 = stream1.collect(Collectors.joining(", ", "[", "]"));
// 拼接成 x | y | z 形式
String result2 = stream2.collect(Collectors.joining(" | ", "", ""));
// 拼接成 x -> y -> z] 形式
String result3 = stream3.collect(Collectors.joining(" -> ", "", ""));
System.out.println(result1);
System.out.println(result2);
System.out.println(result3);

程序输出结果如下：

[Zebe, Hebe, Mary, July, David]
Zebe | Hebe | Mary | July | David
Zebe -> Hebe -> Mary -> July -> David

StringJoiner

List<String> list = Arrays.asList("a", "b", "c", "d", "e", "f", "g");
StringJoiner result = new StringJoiner(delimiter);
for (String str : list) {
    result.add(str);
}
System.out.println(result.toString());

程序输出结果如下：

a, b, c, d, e, f, g

String.join

JDK1.8 为 String 类添加了一个新的静态方法，String.join

List<String> list = Arrays.asList("a", "b", "c", "d", "e", "f", "g");
String delimiter = ",";
String result = String.join(delimiter, list);
System.out.println(result);

String.join 方法的功能内部是通过 StringJoiner 来实现的，String.join (CharSequence, Iterable) 的源码：

public static String join(CharSequence delimiter,
        Iterable<? extends CharSequence> elements) {
     Objects.requireNonNull(delimiter) ;
     Objects.requireNonNull(elements) ;
     StringJoiner joiner = new StringJoiner(delimiter);
     for(CharSequence cs : elements){
         joiner.add(cs);
     }
     return joiner.toString();
}

StringJoiner 除了指定 分隔符 的构造方法，还有一个可以指定 分隔符、前缀和后缀 的构造方法：

StringJoiner(CharSequence delimiter)
StringJoiner(CharSequence delimiter, CharSequence prefix, CharSequence suffix)

示例

List<String> list = Arrays.asList("a", "b", "c", "d", "e", "f", "g");
StringJoiner result = new StringJoiner(delimiter, "{", "}");
for (String str : list) {
    result.add(str);
}
System.out.println(result.toString());

程序输出结果如下：

{a, b, c, d, e, f, g}