本文主要讲述java的饿汉和懒汉设计模式
饿汉和懒汉设计模式的目的：使得该类的对象，只能有一个，不允许其他类，创建该类的对象。
饿汉设计模式
示例代码如下：
public class HungerModel {
public static void main(String[] args) {
// GirlFriend girlFriend1 = new GirlFriend("white", 34);
// GirlFriend girlFriend2 = new GirlFriend("jack", 20);
// System.out.println(girlFriend1);
// System.out.println(girlFriend2);
GirlFriend girlFriend1 = GirlFriend.getInstance();
System.out.println(girlFriend1);
GirlFriend girlFriend2 = GirlFriend.getInstance();
System.out.println(girlFriend2);
System.out.println(girlFriend1 == girlFriend2);
}
}
// 只能有一个女朋友,即只能创建一个girlfriend对象?
class GirlFriend {
private String name;
private int age;
private static GirlFriend girl = new GirlFriend("布尔玛",20);
public static GirlFriend getInstance(){
return girl;
}
private GirlFriend(String name, int age) {
this.name = name;
this.age = age;
}
@Override
public String toString() {
return "GirlFriend{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}运行结果如下：
懒汉设计模式
示例代码如下：
public class LazyModel {
public static void main(String[] args) {
GirlFriend_ girlFriend1 = GirlFriend_.getInstance();
System.out.println(girlFriend1);
GirlFriend_ girlFriend2 = GirlFriend_.getInstance();
System.out.println(girlFriend2);
System.out.println(girlFriend1 == girlFriend2);
}
}
class GirlFriend_ {
private String name;
private int age;
private static GirlFriend_ girlFriend ; // 默认初始值为null
private GirlFriend_(String name, int age) {
this.name = name;
this.age = age;
}
public static GirlFriend_ getInstance(){
if(girlFriend == null){
girlFriend = new GirlFriend_("布尔玛",20);
}
return girlFriend;
}
@Override
public String toString() {
return "GirlFriend_{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}运行结果如下：
饿汉和懒汉模式的区别
饿汉模式，由于直接在类静态成员变量初始化时，创建该类的对象，导致该类对象随着类的存在，一直存在，有可能该对象一直得不到使用，因此饥饿，造成资源浪费；
示例代码如下：
public class HungerModel {
public static void main(String[] args) {
System.out.println(GirlFriend.id);
}
}
// 只能有一个女朋友,即只能创建一个girlfriend对象?
class GirlFriend {
private String name;
private int age;
public static int id = 1001;
private static GirlFriend girl = new GirlFriend("布尔玛",20);
public static GirlFriend getInstance(){
return girl;
}
private GirlFriend(String name, int age) {
this.name = name;
this.age = age;
System.out.println("GirlFriend类的private GirlFriend(String name, int age)构造器被调用");
}
@Override
public String toString() {
return "GirlFriend{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}运行结果如下：
由此看出，没有使用该对象，但是该对象仍然被创建，浪费资源。
懒汉模式，先声明静态变量【对象的引用】，在公共方法【返回对象】时，判断当前对象是否为空，若为空，则创建该对象，返回对象实例，这样，当调用该对象时，才会创建对象，不会造成资源浪费。
示例代码如下：
public class LazyModel {
public static void main(String[] args) {
System.out.println(GirlFriend_.id);
System.out.println(GirlFriend_.getInstance());
}
}
class GirlFriend_ {
private String name;
private int age;
public static int id = 1002;
private static GirlFriend_ girlFriend ; // 默认初始值为null
private GirlFriend_(String name, int age) {
this.name = name;
this.age = age;
System.out.println("GirlFriend_类的private GirlFriend_(String name, int age)构造器被调用");
}
public static GirlFriend_ getInstance(){
if(girlFriend == null){
girlFriend = new GirlFriend_("布尔玛",20);
}
return girlFriend;
}
@Override
public String toString() {
return "GirlFriend_{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}运行结果如下：
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