确保一个类只有一个实例，并提供一个访问它的全局访问点。
类图
实现
懒汉式-线程不安全
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| public class Singleton {
private static Singleton uniqueInstance;
private Singleton() {
}
public static Singleton getInstance() {
if (uniqueInstance == null) {
uniqueInstance = new Singleton();
}
return uniqueInstance;
}
}
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饿汉式-线程安全
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| public class Singleton2 {
private static Singleton2 uniqueInstance = new Singleton2();
private Singleton2() {
}
public static Singleton2 getInstance() {
return uniqueInstance;
}
}
|
双重校验锁-线程安全
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| public class Singleton3 {
private volatile static Singleton3 uniqueInstance;
private Singleton3() {
}
public static Singleton3 getInstance() {
if (uniqueInstance == null) {
synchronized (Singleton3.class) {
if (uniqueInstance == null) {
uniqueInstance = new Singleton3();
}
}
}
return uniqueInstance;
}
}
|