关于java 中 线程加上synchronized关键字的执行顺序问题 报错

"

第一种情况

package com.btmans.thread;

public class TestSync implements Runnable{ int b = 100; public synchronized void m1() throws Exception{ b = 1000; Thread.sleep(5000); System.out.println("b="+b);

}
public synchronized void m2() throws Exception{
    Thread.sleep(3000);
    b = 2000;
}
@Override
public void run() {
    // TODO Auto-generated method stub
    try {
        m1();
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

public static void main(String[] args) throws Exception {
    
    TestSync ts = new TestSync();
    Thread t = new Thread(ts);
    t.start();
    ts.m2();
    System.out.println("=="+ts.b);
    
}

}

输出结果是：
==1000
b=1000

第二种情况：加上下面红色代码部分

package com.btmans.thread;

public class TestSync implements Runnable{
    int b = 100;
    public synchronized void m1() throws Exception{
        System.out.println("m1");"新增部分"
        b = 1000;
        Thread.sleep(5000);
        System.out.println("b="+b);
        
    }
    public synchronized void m2() throws Exception{
        System.out.println("m2");"新增部分"
        Thread.sleep(3000);
        b = 2000;
    }
    @Override
    public void run() {
        // TODO Auto-generated method stub
        try {
            m1();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    
    public static void main(String[] args) throws Exception {
        
        TestSync ts = new TestSync();
        Thread t = new Thread(ts);
        t.start();
        ts.m2();
        System.out.println("=="+ts.b);
        
    }
}

然后结果有时候是
m2
m1
==1000
b=1000
有时候又是
m2
m1
==2000
b=1000

这我就头大了，就只加了一个输出语句而已，为什么加过还会变化呢？加了"synchronized"后，代码的执行顺序到底是怎么样的呢？搞不明白了。