懒汉式
需要使用时再加载
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| public class SingleInstanceLazy {
private static SingleInstanceLazy instance;
private SingleInstanceLazy(){}
public static synchronized SingleInstanceLazy getInstance(){
if (instance == null) {
instance = new SingleInstanceLazy();
}
return instance;
}
}
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饿汉式
类初始化时就加载，调用时直接使用
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| public class SingleInstanceStarvation {
private static final SingleInstanceStarvation instance = new SingleInstanceStarvation();
private SingleInstanceStarvation(){}
public static SingleInstanceStarvation getInstance(){
return instance;
}
}
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双检查DCL式
防止多线程并发访问问题，方法加同步锁
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| public class SingleInstanceDCL {
private static volatile SingleInstanceDCL instance;
private SingleInstanceDCL() {}
public synchronized static SingleInstanceDCL getInstance() {
if (instance == null) {
synchronized (SingleInstanceDCL.class) {
if (instance == null) {
instance = new SingleInstanceDCL();
}
}
}
return instance;
}
}
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静态内部类式
除方法加同步锁外，用静态内部类的方式同样可以防止多线程并发问题
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| public class SingleInstanceStatic {
private SingleInstanceStatic(){}
public static SingleInstanceStatic getInstance(){
return SingleInstanceHolder.instance;
}
private static class SingleInstanceHolder{
private static final SingleInstanceStatic instance = new SingleInstanceStatic();
}
}
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