Java模式之Singleton

单例模式:

目的 --  保证一个类只有一个实例,并提供一个访问它的全局访问点;

public class SingletonTest {
 private SingletonTest(){
  //TODO
  System.out.println("Started!");
 }
 private static SingletonTest instance;
 public static SingletonTest getInstance(){
  if(instance == null){
   instance = new SingletonTest();
  }
  return instance;
 }
 
 public void print(String str){
  System.out.println(str);
 }
 
 public static void main(String[] args){
  SingletonTest test = SingletonTest.getInstance();
  test.print("hello world");
  test.print("----------------------------------");
  SingletonTest test2 = SingletonTest.getInstance();
  test2.print("Time 2");
 }
}

简单的例子如上,运行结果:

Started!
hello world
----------------------------------
Time 2

"started"只打印出一次;