JAVA设计模式之【单例模式】

任务管理器案例

1.单例类

package Singleton;/*** Created by Jim on 2016/9/28.*/
public class TaskManager {private static TaskManager tm = null;private TaskManager() {System.out.println("创建任务管理器");}public void displayProcesses() {System.out.println("显示进程");}public void displayServices() {System.out.println("显示服务");}public static TaskManager getInstance() {if (tm == null) {tm = new TaskManager();}return tm;}}

2.客户端

package Singleton;public class Client
{public static void main(String args[]){try{TaskManager tm = TaskManager.getInstance();tm.displayProcesses();tm.displayServices();TaskManager tm2 = TaskManager.getInstance();tm2.displayProcesses();tm2.displayServices();}catch(Exception e){System.out.println(e.getMessage());}}
}

身份证办理案例

1.单例类

package Singleton;/*** Created by e550 on 2016/9/29.*/
public class IdentityCardNo {private static IdentityCardNo instance=null;private String no;private IdentityCardNo(){}public static IdentityCardNo getInstance(){if(instance==null){System.out.println("第一次办理身份证，分配新号码！");instance=new IdentityCardNo();instance.setIdentityCardNo("No400011112222");}else{System.out.println("重复办理身份证，获取旧号码！");}return instance;}private void setIdentityCardNo(String no){this.no=no;}public String getIdentityCardNo(){return this.no;}
}

2.客户端类

package Singleton;public class Client
{public static void main(String args[]){try{IdentityCardNo no1,no2;no1=IdentityCardNo.getInstance();no2=IdentityCardNo.getInstance();System.out.println("身份证号码是否一致：" + (no1==no2));String str1,str2;str1=no1.getIdentityCardNo();str2=no1.getIdentityCardNo();System.out.println("第一次号码：" + str1);System.out.println("第二次号码：" + str2);System.out.println("内容是否相等：" + str1.equalsIgnoreCase(str2));System.out.println("是否是相同对象：" + (str1==str2));}catch(Exception e){System.out.println(e.getMessage());}}
}

执行结果：

第一次办理身份证，分配新号码！
重复办理身份证，获取旧号码！
身份证号码是否一致：true
第一次号码：No400011112222
第二次号码：No400011112222
内容是否相等：true
是否是相同对象：true

打印池

1.打印池类

package SpoolerSingleton;public class PrintSpoolerSingleton
{private static PrintSpoolerSingleton instance=null; // 打印池private PrintSpoolerSingleton(){}public static PrintSpoolerSingleton getInstance() throws PrintSpoolerException{if(instance==null){System.out.println("创建打印池！");instance=new PrintSpoolerSingleton();}else{throw new PrintSpoolerException("打印池正在工作中！");}return instance;}public void manageJobs(){System.out.println("管理打印任务！");}
}

2.异常辅助类

package SpoolerSingleton;public class PrintSpoolerException extends Exception
{public PrintSpoolerException(String message){super(message);}
}

3.客户端类

package SpoolerSingleton;public class Client
{public static void main(String a[]){PrintSpoolerSingleton ps1,ps2;try{ps1=PrintSpoolerSingleton.getInstance();ps1.manageJobs();}catch(PrintSpoolerException e){System.out.println(e.getMessage());}System.out.println("--------------------------");try{ps2=PrintSpoolerSingleton.getInstance();ps2.manageJobs();}catch(PrintSpoolerException e){System.out.println(e.getMessage());}}
}

执行结果：