剑指offer4J【C2 P2】 实现懒汉单例

线程安全懒汉单例一般继续双检查，检查-》加锁-》检查-》构建

public class Problem02 {
    private Problem02 singleton = null;

    private Problem02() {
    }
    public Problem02 getSingleton(){
        if(singleton==null){
            synchronized (Problem02.class){
                if(singleton==null){
                    singleton = new Problem02();
                }
            }
        }
        return singleton;
    }
}

源码: 剑指offer4J