史上最简单的一道面试题！坑人吧

Posted 2020-11-10 ttzzyy

把下面a，b值互换，使打印结果为a=2,b=1.

import java.lang.reflect.Field;

/**
 * Created by 70416 on 2018/4/7.
 */
public class App {
    public static void swap(Integer i1,Integer i2) throws NoSuchFieldException, IllegalAccessException {
      .....
    }
    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException {
        Integer a=1,b=2;
        System.out.println("开始a="+a+",b="+b);
        swap(a,b);
        System.out.println("结束a="+a+",b="+b);
    }
}

Field field = Integer.class.getDeclaredField("value");
field.setAccessible(true);
int tmp = i1.intValue();    
field.set(i1,i2.intValue());
field.set(i2,tmp);

import java.lang.reflect.Field;

/**
 * Created by 70416 on 2018/4/7.
 */
public class App {
    public static void swap(Integer i1,Integer i2) throws NoSuchFieldException, IllegalAccessException {
        Field field = Integer.class.getDeclaredField("value");
        field.setAccessible(true);
        Integer tmp = new Integer(i1.intValue());
        // int tmp = i1.intValue();    //Integer -127----128里的值这个就不行，指针指向了缓存里的值。
        field.set(i1,i2.intValue());
        field.set(i2,tmp);

    }
    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException {
        Integer a=1,b=2;
//        System.out.println(a==b); //Integer -127----128里的相同值，答案为true，超出缓存为false。
        System.out.println("开始a="+a+",b="+b);
        swap(a,b);
        System.out.println("结束a="+a+",b="+b);
    }
}