单例模式之饿汉式
//饿汉式
public class Singleton1 {
private Singleton1() {
}
private static Singleton1 instance = new Singleton1();
public static Singleton1 getInstance(){
return instance;
}
}
单例模式之懒汉式
//懒汉式、支持多并发、效率低
public class Singleton3 {
private Singleton3() {
}
private static Singleton3 instance = null;
public synchronized static Singleton3 getInstance(){
if (instance == null){
instance = new Singleton3();
}
return instance;
}
}
单例模式之双锁式
//double checked locking、支持多并发、效率高、添加volatile关键字
public class Singleton4 {
private Singleton4() {
}
private volatile static Singleton4 instance = null;
public static Singleton4 getInstance(){
if (instance == null){//1
synchronized (Singleton4.class) {
if (instance == null)//2
instance = new Singleton4();
}
}
return instance;
}
}
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