常用面试代码小Demo

java递归的简单实现方式

递归计算100以内的数累计求和

public class TestDemo{

    public static void main(String[] args){
          System.out.println(sum(100));
    }

    public static int sum(int num){

        if(num == 1){
              return 1;
        }

        return num + sum(num - 1);
    }
}

记住：使用递归的时候，递归方法一定要有结束条件

单例模式代码

懒汉模式（方法同步----添加同步锁）

public class TestDemo{

    private static TestDemo instance;

    private TestDemo(){}

    public static synchronized TestDemo getInstance(){

        if(instance == null){
            instance = new TestDemo();
        }

        return instance;
    }
}

枚举

public enum TestDemo{

    INSTANCE;

    public void whateverMethod(){

    }
}

静态内部类

public class Singleton {

    private Singleton() {}

    private static class SingletonInstance {
        private static final Singleton INSTANCE = new Singleton();
    }

    public static Singleton getInstance() {
        return SingletonInstance.INSTANCE;
    }
}