Java多线程之线程范围内共享变量的概念与作用
要实现线程范围内的数据共享，就是说不管是A模块还是B模块，如果它们现在在同一个线程上运行，它们操作的数据应该是同一个，下面的做法就不行：
package javaplay.thread.test;
import java.util.Random;
public class ThreadScopeShareData {
private static int data = 0;
public static void main(String[] args) {
for (int i = 0; i < 2; i++) {
new Thread(new Runnable() {
@Override
public void run() {
data = new Random().nextInt();
System.out.println(Thread.currentThread().getName() + " has put data : " + data);
new A().get();
new B().get();
}
}).start();
}
}
static class A {
public void get() {
System.out.println("A from " + Thread.currentThread().getName() + " get data : " + data);
}
}
static class B {
public void get() {
System.out.println("B from " + Thread.currentThread().getName() + " get data : " + data);
}
}
}
output:
Thread-0 has put data : 840132982
Thread-1 has put data : -1767656158
A from Thread-0 get data : -1767656158
A from Thread-1 get data : -1767656158
B from Thread-0 get data : -1767656158
B from Thread-1 get data : -1767656158在这个线程范围内，不管哪个模块去取这个变量拿到的都是同一个变量；换了另外一个线程就是另外一份数据了；即线程内共享，线程外独立；
package javaplay.thread.test;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;
public class ThreadScopeShareData {
private static int data = 0;
private static Map<Thread, Integer> threadData = new HashMap<Thread, Integer>();
public static void main(String[] args) {
for (int i = 0; i < 2; i++) {
new Thread(new Runnable() {
@Override
public void run() {
int data = new Random().nextInt();
System.out.println(Thread.currentThread().getName() + " has put data : " + data);
threadData.put(Thread.currentThread(), data);
new A().get();
new B().get();
}
}).start();
}
}
static class A {
public void get() {
int data = threadData.get(Thread.currentThread());
System.out.println("A from " + Thread.currentThread().getName() + " get data : " + data);
}
}
static class B {
public void get() {
int data = threadData.get(Thread.currentThread());
System.out.println("B from " + Thread.currentThread().getName() + " get data : " + data);
}
}
}
output:
Thread-0 has put data : -74463225
Thread-1 has put data : -2119679267
A from Thread-1 get data : -2119679267
A from Thread-0 get data : -74463225
B from Thread-1 get data : -2119679267
B from Thread-0 get data : -74463225
数据库的连接就是一个典型的应用
