java try-catch

/**
 * @author  wang
 * @description 直接复制下来运行。
 * @create 2022/3/4 15:14
 */

public class TTT {
    public static int sum1() {
        int firstNum = 1;
        int secondNum = 2;
        int result = 0;
        try {
            //计算结果
            result = firstNum + secondNum;
            return result;
        } finally {
            System.out.println("sum1() finally块被执行了！");
        }
    }
    public static int sum2() {
        int firstNum = 1;
        int secondNum = 2;
        int result = 0;
        try {
        //计算结果
            result = firstNum + secondNum;
            return result;
        } finally {
            System.out.println("sum2() finally块被执行了！");
            result = 777;
        }
    }
    public static int sum3() {
        int firstNum = 1;
        int secondNum = 2;
        int result = 0;
        try {
            result = firstNum + secondNum;
            return result;
        } finally {
            System.out.println("sum3() finally块被执行了！");
            result = 7;
            return result;
        }
    }
    public static int sum4() {
        int firstNum = 1;
        int secondNum = 2;
        int result = 0;
        try {
            //计算结果
            result = firstNum + secondNum;
            //制造异常
            int i = 1 / 0;
            return result;
        } catch (Exception e) {
            System.out.println(e.getMessage());
        } finally {
            System.out.println("sum4() finally块被执行了！");
            result = 7;
            return result;
        }
    }
    public static int sum5() {
        int firstNum = 1;
        int secondNum = 2;
        int result = 0;
        try {
            //计算结果
            result = firstNum + secondNum;
            //系统退出，，，finally不再执行
            System.exit(1);
            return result;
        } finally {
            System.out.println("sum5() finally块被执行了！");
            result = 7;
            return result;
        }
        //编译器会报错，因为无法执行到此处
        //return 1111;
    }
    public static void main(String[] args) {
        System.out.println(TTT.sum1());
        System.out.println(TTT.sum2());
        System.out.println(TTT.sum3());
        System.out.println(TTT.sum4());
        System.out.println(TTT.sum5());
//结论：
//try { return A }catch{ }finally{ } 原引用为A，会”备份“A，记为B （A,B都在栈上）
// 当A是基本类型时，不管你如何对A进行操作，返回的是B的值,除非你在fianlly中 也return A 则B值会被更新。 
//当A是引用类型。你备份的B和A指向的是堆中同一块内存，你用A任意引用操作对象，返回的都是更改后的同一个对象。

    }
}

运行结果：

sum1() finally块被执行了！
3
sum2() finally块被执行了！
3
sum3() finally块被执行了！
7
/ by zero
sum4() finally块被执行了！
7