Java 单例总结
2024-09-01 06:42:14
1：懒汉式，不保证线程安全
package com.yan.singleton;
public class LazySingleton {
private static final LazySingleton instance = null;
private LazySingleton(){}
public static LazySingleton getLazySingleton(){
if(null==instance){
return new LazySingleton();
}
return instance;
}
}
2：饿汉式，线程安全
package com.yan.singleton;
public class HungrySingleton {
private HungrySingleton(){}
private static final HungrySingleton instance = new HungrySingleton();
public static HungrySingleton getInstance(){
return instance;
}
}
3：静态内部类，线程安全
package com.yan.singleton;
public class InnerClassSingleton {
private InnerClassSingleton(){}
public static final InnerClassSingleton getInstance(){
return InnerClassSingletonHolder.INSTANCE;
}
private static class InnerClassSingletonHolder{
private static final InnerClassSingleton INSTANCE = new InnerClassSingleton();
}
}
4：枚举，线程安全，可以反序列化（推荐此种方式）JDK1.5之后才可以使用
package com.yan.singleton;
public enum EnumSingleton {
INSTANCE;
public void todo(){
System.out.println("todo");
}
}
方式1,2,3都可以使用反射机制来破坏其单例特性，采用枚举类型可以避免反射的破坏。
例如：
package com.yan.test; import com.yan.singleton.LazySingleton;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.util.logging.Level;
import java.util.logging.Logger; public class Test { public static void main(String[] args) { Constructor<LazySingleton>cs ; try {
cs = (Constructor<LazySingleton>)
Class.forName("com.yan.singleton.LazySingleton")
.getDeclaredConstructor(); cs.setAccessible(true);//得到私有访问权限，如果不设置，则无法实例化对象 LazySingleton ls = cs.newInstance(); System.out.println("===ls:"+ls);
System.out.println("===ls:"+cs.newInstance()); } catch (ClassNotFoundException ex) {
Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
}catch (SecurityException ex) {
Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
} catch (IllegalArgumentException ex) {
Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
} catch (InvocationTargetException ex) {
Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
} catch (NoSuchMethodException ex) {
Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
} } }
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