1.饿汉式
/** 线程安全，调用效率高。 但是，不能延时加载**/
public class SingletonTest {
private static SingletonTest s =new SingletonTest();
private static SingletonTest getInstance() {
return s;
}
}
2.懒汉式（延时加载，懒加载，真正用的时候才加载！，但是每次调用的时候都要同步，并发效率降低了）
public class SingletonTest {
private static SingletonTest s;
public static synchronized SingletonTest getInstance() {
if(s==null) {
s = new SingletonTest();
}
return s;
}
}
3.双重检测锁(不是每次获取对象时都进行同步，只有第一次才同步创建以后就没必要了)
private static SingletonTest instance =null;
public static synchronized SingletonTest getInstance() {
if(instance==null) {
SingletonTest si;
synchronized (SingletonTest.class) {
si = instance;
if(si == null) {
synchronized (SingletonTest.class) {
si = new SingletonTest();
}
}
instance =si;
}
}
return instance;
}
4.静态内部类（高效调用和延迟加载的优势）
private static class SingletonClassInstance{
private static final SingletonTest instance =new SingletonTest();
}
public static SingletonTest getInstance() {
return SingletonClassInstance.instance;
}
5 枚举类
public enum SingletonClassInstance （）{
INSTANCE;
public void operation () {
}
}
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