Java-设计模式-单例模式-饿汉模式、懒汉模式

//-------------------------------------------------------------饿汉模式--开始-----------------------------------------------------------
package com.study.DesignPattern01;
/**
 * 创建一个饿汉模式的单例
 * @author ZLHome
 *有些对象，我们只需要一个，如果多了，那么就可能导致数据不一致，
    占用资源过多等等，比如：
        配置文件、工具类、线程池、缓存、日志对象
 */
public class Singleton {
    //1、构造方法私有化（这样类就不能被实例化了）
    private Singleton(){
        System.out.println("实例化Singleton类");
    }
    
    //2、实例化单例对象，对象为静态的（这样就只会实例化一次），私有的（安全，外部不能直接Singleton.instance调用）
    private static Singleton instance = new Singleton();
    
    //3、提供一个静态方法（静态方法，类可以直接调用），用于获取单例
    public static Singleton getInstance(){
        return instance;
    }
}
//---------------------------------------------------------------------------------------------
package com.study.DesignPattern01;

import org.junit.After;
import org.junit.AfterClass;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;

public class SingletonTest {

    @BeforeClass
    public static void setUpBeforeClass() throws Exception {
        System.out.println("Junit开始BeforeClass...");
    }

    @AfterClass
    public static void tearDownAfterClass() throws Exception {
        System.out.println("Junit过后AfterClass...");
    }

    @Before
    public void setUp() throws Exception {
        System.out.println("Junit开始Before...");
    }

    @After
    public void tearDown() throws Exception {
        System.out.println("Junit过后After...");
    }

    @Test
    public void test() {
        System.out.println("Junit开始...");
        Singleton instance = Singleton.getInstance();
        Singleton instance1 = Singleton.getInstance();
        System.out.println("是否相等："+(instance==instance1));
    }

}
//-------------------------------------------------------------饿汉模式--结束-----------------------------------------------------------



//============================================================懒汉模式--开始============================================================
package com.study.DesignPattern01;

public class Singleton1 {
    //1、将构造方法设置为私有（这样类就不能被外部实例化了）
    private Singleton1(){
        System.out.println("实例化Singleton1");
    }
    
    //2、申明单例对象
    private static Singleton1 instance;
    
    //3、提供一个静态方法（静态方法属于类），用于外部调用
    public static Singleton1 getInstance(){
        if(instance==null){
            System.out.println("第一次实例化Singleton1对象");
            instance=new Singleton1();
        }
        return instance;
    }
}


//============================================================

package com.study.DesignPattern01;

import org.junit.After;
import org.junit.AfterClass;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;

public class Singleton1Test {

    @BeforeClass
    public static void setUpBeforeClass() throws Exception {
        System.out.println("Junit开始BeforeClass...");
    }

    @AfterClass
    public static void tearDownAfterClass() throws Exception {
        System.out.println("Junit过后AfterClass...");
    }

    @Before
    public void setUp() throws Exception {
        System.out.println("Junit开始Before...");
    }

    @After
    public void tearDown() throws Exception {
        System.out.println("Junit过后After...");
    }

    @Test
    public void test() {
        System.out.println("Junit开始...");
        Singleton1 instance = Singleton1.getInstance();
        Singleton1 instance1 = Singleton1.getInstance();
        System.out.println("是否相等："+(instance==instance1));
    }

}


//============================================================懒汉模式--结束============================================================