StringBuilder线程不安全效果演示

public static void main(String[] args) throws InterruptedException {
    System.out.println("StringBuffer: ");
    for (int i = 0; i < 10; i++) {
        StringBuffer stringBuffer = new StringBuffer();
        Thread thread1 = new Thread(() -> {
            for (int j = 0; j < 5000; j++) {
                stringBuffer.append("a");
            }
        });
        Thread thread2 = new Thread(() -> {
            for (int j = 0; j < 5000; j++) {
                stringBuffer.append("b");
            }
        });
        thread1.start();
        thread2.start();
        thread1.join();
        thread2.join();
        System.out.println(stringBuffer.length());
    }

    System.out.println("StringBuilder: ");
    for (int i = 0; i < 10; i++) {
        StringBuilder stringBuilder = new StringBuilder();
        Thread thread1 = new Thread(() -> {
            for (int j = 0; j < 5000; j++) {
                stringBuilder.append("1");
            }
        });
        Thread thread2 = new Thread(() -> {
            for (int j = 0; j < 5000; j++) {
                stringBuilder.append("1");
            }
        });
        thread1.start();
        thread2.start();
        thread1.join();
        thread2.join();
        System.out.println(stringBuilder.length());
    }
}

Output:

StringBuffer: 
10000
10000
10000
10000
10000
10000
10000
10000
10000
10000
StringBuilder: 
6106
6184
6502
6506
5910
6248
6203
7160
6327
7650

Reference

为什么说StringBuilder线程不安全