1.在类中方法上加上
synchronized关键字，是对整个对象加锁，当一个线程访问带有synchronized的方法时，其他带有synchronized的方法的访问就都会阻塞。
样例：
|
public class ThreadTest {
public static void main(String[] args) {
Stu stu = new Stu();
StuThread1 t1 = new StuThread1(stu);
t1.start();
StuThread2 t2 = new StuThread2(stu);
t2.start();
}
}
class StuThread1 extends Thread {
Stu stu;
public StuThread1(Stu stu) {
this.stu = stu;
}
public void run() {
stu.read1();
}
}
class StuThread2 extends Thread {
Stu stu;
public StuThread2(Stu stu) {
this.stu = stu;
}
public void run() {
stu.read2();
}
}
class Stu {
public synchronized void read1() {
System.out.println("read1 begin");
try {
Thread.currentThread().sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("read1 end");
}
public synchronized void read2() {
System.out.println("read2 begin");
try {
Thread.currentThread().sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("read2 end");
}
}
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打印结果为（两个线程是顺序执行的）：
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read1 begin
read1 end
read2 begin
read2 end
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如果去掉read2前面的synchronized关键字，打印为（线程出现了交叉执行）：
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read1 begin
read2 begin
read2 end
read1 end
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修改read2方法，
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public void read2() {
synchronized(this)
{
System.out.println("read2 begin");
try {
Thread.currentThread().sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("read2 end");
}
}
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对this进行加锁，结果同一次，线程是顺序执行的。
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