定义：确保某一个类只有一个实例，而且自行实例化并向整个系统提供整个实例。
使用场景：确保某个类有且只有一个对象的场景，避免产生多个对象消耗过多的资源，或者某种类型的对象应该有且只有一个。
懒汉式
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| public class Singleton {
private static Singleton sInstance = null;
private Singleton(){
}
public void init(){}
public static synchronized Singleton getInstance(){
if (sInstance == null){
sInstance = new Singleton();
}
return sInstance;
}
}
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饿汉式
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| public class Singleton {
private final static Singleton INSTANCE = new Singleton();
private Singleton(){}
public static Singleton getInstance(){
return INSTANCE;
}
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DCL(Double Check Lock)
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| public class Singleton {
private static volatile Singleton mInstance = null;
private Singleton(){}
public void init(){}
public static Singleton getInstance(){
if (mInstance==null){
synchronized (Singleton.class){
if (mInstance == null){
mInstance = new Singleton();
}
}
}
return mInstance;
}
}
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静态内部类单例模式
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| public class Singleton {
private Singleton(){
}
public void init(){}
public static Singleton getInstance(){
return SingletonHolder.sInstance;
}
private static class SingletonHolder{
private static final Singleton sInstance = new Singleton();
}
}
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枚举单例
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| public enum Singleton {
INSTANCE;
public void init(){}
}
|