StringJoiner学习和使用

Posted 2022-10-21 泡^泡

StringJoiner是JDK1.8新添加的新特性,字符串拼接神器，比StringBuilder更加方便好用。

类结构图

prefix：拼接后的字符串前缀
delimiter：拼接时的字符串分隔符
suffix：拼接后的字符串后缀
value：拼接后的值
emptyValue：空值的情况，value为null时返回
setEmptyValue()：设置空值
toString()：转换成String
add()：添加字符串
merge():从另一个StringJoiner合并
length()：长度（包括前后缀）

构造方法

StringJoiner提供了两个构造器，一个必须带分隔符，另一个必须带分隔符、前缀、后缀

public StringJoiner(CharSequence delimiter) 
        this(delimiter, "", "");
    

 public StringJoiner(CharSequence delimiter,
                        CharSequence prefix,
                        CharSequence suffix) 
        Objects.requireNonNull(prefix, "The prefix must not be null");
        Objects.requireNonNull(delimiter, "The delimiter must not be null");
        Objects.requireNonNull(suffix, "The suffix must not be null");
        // make defensive copies of arguments
        this.prefix = prefix.toString();
        this.delimiter = delimiter.toString();
        this.suffix = suffix.toString();
        this.emptyValue = this.prefix + this.suffix;
    

分隔符案例

package com;

import java.util.StringJoiner;
/**
 * JDK1.8特性
 */
public class StringJoinerTest 
    public static void main(String[] args) 
        //分隔离
        StringJoiner str = new StringJoiner(",");
        str.add("hello");
        str.add("world");
        System.out.println(str);
    

前后缀案例

package com;

import java.util.StringJoiner;
/**
 * JDK1.8特性
 */
public class StringJoinerTest 
    public static void main(String[] args) 
        //前后缀案例
        StringJoiner str = new StringJoiner(",","【","】");
        str.add("hello");
        str.add("world");
        System.out.println(str);
    

空值处理

package com;

import java.util.StringJoiner;
/**
 * JDK1.8特性
 */
public class StringJoinerTest 
    public static void main(String[] args) 
        //空值
        StringJoiner str = new StringJoiner(",");
        System.out.println(str.toString());
        str = new StringJoiner(",","[","]");
        System.out.println(str.toString());
        str = new StringJoiner(",","[","]");
        str.setEmptyValue("null");
        System.out.println(str.toString());