Java 学习笔记之 实例变量与线程安全
2024-09-01 08:26:05
实例变量与线程安全：
不共享数据：
public class NoSharedThread extends Thread {
private int count = 5;
public NoSharedThread(String name){
super();
this.setName(name);
}
@Override
public void run() {
super.run();
while (count > 0){
count--;
System.out.println("Thread name: " + Thread.currentThread().getName() + ", count: " + count);
}
}
}
public class ThreadRunMain {
public static void main(String[] args) {
testSharedSafeThead();
}
public static void testNoSharedThread() {
NoSharedThread a = new NoSharedThread("a");
NoSharedThread b = new NoSharedThread("b");
NoSharedThread c = new NoSharedThread("c");
a.start();
b.start();
c.start();
}
}
运行结果：
可见线程之间没有互相干扰，都在操作自己的count变量。
共享数据：
public class SharedThread extends Thread{
private int count = 5;
public SharedThread(String name) {
super();
this.setName(name);
}
@Override
public void run() {
super.run();
count--;
System.out.println("Thread name: " + Thread.currentThread().getName() + ", count: " + count);
}
}
public class ThreadRunMain {
public static void main(String[] args) {
testSharedThead();
}
public static void testSharedThead(){
SharedThread st = new SharedThread("SharedThread");
Thread a = new Thread(st,"a");
Thread b = new Thread(st,"b");
Thread c = new Thread(st,"c");
Thread d = new Thread(st,"d");
Thread e = new Thread(st,"e");
a.start();
b.start();
c.start();
d.start();
e.start();
}
}
运行结果：
可见线程之间互相干扰，产生count值一样的情况，非线程安全的问题出现。
共享数据线程安全：
public class SharedSafeThread extends Thread{
private int count = 5;
public SharedSafeThread(String name) {
super();
this.setName(name);
}
@Override
public synchronized void run() {
super.run();
count--;
System.out.println("Thread name: " + Thread.currentThread().getName() + ", count: " + count);
}
}
public class ThreadRunMain {
public static void main(String[] args) {
testSharedSafeThead();
}
public static void testSharedSafeThead(){
SharedSafeThread sst = new SharedSafeThread("SharedSafeThread");
Thread a = new Thread(sst,"a");
Thread b = new Thread(sst,"b");
Thread c = new Thread(sst,"c");
Thread d = new Thread(sst,"d");
Thread e = new Thread(sst,"e");
a.start();
b.start();
c.start();
d.start();
e.start();
}
}
运行结果：
可见线程之间没有互相干扰，count值没有重复，线程安全。
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