싱글톤 패턴
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객체 생성, 싱글톤 클래스 생성, 인스턴스 객체 생성, new 없이 직접 사용하는 모드인 빌더 모드에 속합니다.
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역할은 싱글톤 클래스와 액세스 클래스로 나뉩니다.
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배고프고 게으른
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//单例分为 饿汉式和懒汉式 //饿汉式分为: //静态变量 //静态代码块 //懒汉式分为: //线程不安全 //线程安全 //双检锁 //内部类 //枚举 //单例的特点 //1.构造方法私有化 //2.提供一个返回单例对象本身的公共方法 //3.提供一个静态私有的变量 public class SingletonsTest { public static void main(String[] args) { Singleton singleton=Singleton.getInstance(); Singleton singleton2=Singleton.getInstance(); } } // 饿汉式-静态变量 class Singleton { //3.提供一个静态私有的变量 private static Singleton instance = new Singleton(); //1.构造器私有化 private Singleton() { } //2.提供一个返回单例对象本身的公共方法 public static Singleton getInstance() { return instance; } }
public class SingletonTest2 {
public static void main(String[] args) {
Singleton1 singleton=Singleton1.getInstance();
Singleton1 singleton1=Singleton1.getInstance();
System.out.println(singleton==singleton1);
}
}
class Singleton1 {
private static Singleton1 instance;
//静态代码块版本的 饿汉式
static {
instance = new Singleton1();
}
private Singleton1() {
}
public static Singleton1 getInstance() {
return instance;
}
}
게으른
import java.util.Properties;
public class SingletonTest3 {
public static void main(String[] args) {
// Singleton3 singleton3 = Singleton3.getInstance();
// Singleton3 singleton4 = Singleton3.getInstance();
//
// System.out.println(singleton3 == singleton4);
}
}
//枚举:构造器私有
enum Color {
Red(1), Blue(1), Green(1);
private Color(int n){
}
public void show() {
}
}
//懒汉式 枚举 可以防止反射 每一个枚举类都是Enum的子类 最安全的最好的懒汉单例
enum SingletonEnum{
Instance;
private SingletonEnum(){
System.out.println("枚举类被实例化");
}
final static Properties prop=new Properties();
public static Properties getProperties(){
prop.setProperty("driver","com.mysql.jdbc.Driver");
prop.setProperty("user","root");
return prop;
}
}
//懒汉式 内部类
class Singleton3_4 {
private static Singleton3_4 instance;
private Singleton3_4() {
}
private static class SingletonHolder {
private static Singleton3_4 INSTANCE = new Singleton3_4();
}
public static Singleton3_4 getINSTANCE() {
if (instance == null) {
instance = SingletonHolder.INSTANCE;
}
return instance;
}
}
//懒汉式 线程安全(优化法)(双重验证)
class Singleton3_3 {
private static Singleton3_3 instance;
private Singleton3_3() {
}
public static Singleton3_3 getInstance() {
if (instance == null) {
//为空 加了判断就不用再创建对象了
//只锁关键部分
synchronized (Singleton3_3.class) {
if (instance == null) {
instance = new Singleton3_3();
}
}
}
return instance;
}
}
//懒汉式 线程安全
class Singleton3_2 {
private static Singleton3_2 instance;
private Singleton3_2() {
}
public synchronized static Singleton3_2 getInstance() {
//synchronized static 锁的是字节码文件 .class 字节码文件是唯一的
//synchronized 锁的是当前对象
if (instance == null) {
instance = new Singleton3_2();
}
return instance;
}
}
//懒汉式 线程不安全
class Singleton3 {
private static Singleton3 instance;
private Singleton3() {
}
public static Singleton3 getInstance() {
if (instance == null) {
instance = new Singleton3();
}
return instance;
}
}