一、多线程下的单例设计模式
利用双重判断的形式解决懒汉式的安全问题和效率问题
//饿汉式
/*class Single
{
private static final Single t = new Single();
private Single(){}
public static Single getInstance()
{
return t;
}
}
*/
//懒汉式
class Single
{
private static Single t = null;
private Single(){}
public static Single getInstance()
{
if(t==null)//解决效率问题
{
synchronized(Single.class)//解决安全问题
{
if(t==null)
t = new Single();
}
}
return t;
}
}
二、死锁示例
死锁：常见就是，同步的嵌套
面试时，会让写死锁程序，只要写的出来，就说明死锁已经理解
class Deadlock implements Runnable
{
private boolean flag;
public Deadlock(boolean flag) {
// TODO Auto-generated constructor stub
this.flag = flag;
}
public void run()
{
if(flag)
{
while(true)
synchronized (lock.A_LOCK) {
System.out.println("if...alock");
synchronized (lock.B_LOCK) {
System.out.println("if...block");
}
}
}
else {
while(true)
synchronized (lock.B_LOCK) {
System.out.println("else...block");
synchronized (lock.A_LOCK) {
System.out.println("else...alock");
}
}
}
}
}
class lock
{
public static final Object A_LOCK = new Object();
public static final Object B_LOCK = new Object();
}
class Main
{
public static void main(String[] args)
{
Deadlock t1 = new Deadlock(true);
Deadlock t2 = new Deadlock(false);
Thread j1 = new Thread(t1);
Thread j2 = new Thread(t2);
j1.start(); j2.start();
}
}锁上了，Thread-0拿a锁，Thread-1拿b锁
JAVA学习第二十五课（多线程（四））- 单例设计模式涉及的多线程问题
原文：http://blog.csdn.net/wjw0130/article/details/39941593