字符串拼接

字符串拼接

方式

1. +，

2. Join，

3. StringBuffer，(线程安全, appent()方法使用了sychronized，线程安全)

4. StringBuilder或String.concat()，线程不安全

效率

public static void main(String[] args) {
        //+
        long tick01 = System.currentTimeMillis();
        String tar = "";
        for (int i = 0; i < 1000000; i++) {
            tar += i;
        }
        long tick02 = System.currentTimeMillis();
        System.out.println(tar.length() + ", +  cost: " + (tick02 - tick01) );
​
        //Join
        ArrayList<String> lst = new ArrayList<>();
        for (int i = 0; i < 1000000; i++) {
            lst.add(String.valueOf(i));
        }
        long tick11 = System.currentTimeMillis();
        String tar2 = String.join(",", lst);
        long tick12 = System.currentTimeMillis();
        System.out.println(tar2.length() + ", String.join cost: " + (tick12 - tick11) );
​
        //StringBuffer
        StringBuffer sb = new StringBuffer();
        long tick21 = System.currentTimeMillis();
        for (int i = 0; i < 1000000; i++) {
            sb.append(i);
        }
        String tar3 = sb.toString();
        long tick22 = System.currentTimeMillis();
        System.out.println(tar3.length() + ", StringBuffer cost: " + (tick22 - tick21) );
​
        //StringBuilder
        StringBuilder sbd = new StringBuilder();
        long tick31 = System.currentTimeMillis();
        for (int i = 0; i < 1000000; i++) {
            sbd.append(i);
        }
        String tar4 = sbd.toString();
        long tick32 = System.currentTimeMillis();
        System.out.println(tar4.length() + ", StringBuilder cost: " + (tick32 - tick31) );
​
    }
​
//结果
5888890, +  cost: 1029756
6888889, String.join cost: 33
5888890, StringBuffer cost: 22
5888890, StringBuilder cost: 22

• StringBuilder 和 StringBuffer效率最高

• 直接字符串拼接效率最低

结论