try catch finally各种情况的执行顺序（示例）

Posted 2023-02-21 洛雪_

比较有意思的，基础的，容易忽略的小例子，开发的时候要注意

上例子

示例1

public static void main(String[] args) 
        int i = test1();
        System.out.println("main " + i);
    

    private static int test1()
        int i=0;
        try 
            i++;
            System.out.println("try- " + i);
        catch (Exception e)
            i++;
            System.out.println("exception: " + i);
        finally 
            i++;
            System.out.println("finally: " + i);
        

        return i;
    

执行结果可以看出， 执行了try 加一，finally加一，最后返回i=2

try- 1
finally: 2
main 2

---

示例2 

private static int test1()
        int i=0;
        try 
            i++;
            System.out.println("try- " + i);
            return i;
        catch (Exception e)
            i++;
            System.out.println("exception: " + i);
        finally 
            i++;
            System.out.println("finally: " + i);
        
        return i;
    

在try中加了return，可以看出，try加一，保存了i，finally加一，返回的i是try中刚刚保存的i=1

try- 1
finally: 2
main 1

---

示例3 

private static int test1()
        int i=0;
        try 
            i++;
            System.out.println("try- " + i);
            int a = 1/0;
            return i;
        catch (Exception e)
            i++;
            System.out.println("exception: " + i);
        finally 
            i++;
            System.out.println("finally: " + i);
        
        return i;
    

 如果在try中加了1/0会导致异常，catch加一，finally加一，最后返回i=3

try- 1
exception: 2
finally: 3
main 3

同理显而易见，如果catch中加了return i；那么try加一，catch加一为2，即使finally中加一也不会返回回去

try- 1
exception: 2
finally: 3
main 2

---

下面我们试一下引用类型

示例4

    private static List<Integer> test1()
        List<Integer> list = new ArrayList<>();
        try 
            list.add(1);
            System.out.println("try- " + list);
        catch (Exception e)
            list.add(2);
            System.out.println("exception: " + list);
        finally 
            list.add(3);
            System.out.println("finally: " + list);
        
        return list;
    

可以看出和示例1是没有区别的，执行了try，finally，最后返回1,3 

 try- [1]
finally: [1, 3]
main [1, 3]

---

private static List<Integer> test1()
        List<Integer> list = new ArrayList<>();
        try 
            list.add(1);
            System.out.println("try- " + list);
            return list;
        catch (Exception e)
            list.add(2);
            System.out.println("exception: " + list);
        finally 
            list.add(3);
            System.out.println("finally: " + list);
        
        return list;
    

 try中加了return list;但是返回仍是1,3，为什么？因为这里用的是引用类型，try中return存的是引用地址，而不是变量本身，所以在finally中add时是生效的（这里一定要注意！）

try- [1]
finally: [1, 3]
main [1, 3]

---

 同理，在try中后面加 int a = 1/0; 结果就是try，catch，finally全部执行了，不论里面有没有return

try- [1]
exception: [1, 2]
finally: [1, 2, 3]
main [1, 2, 3]

总结

        所以大家可以看到，引用类型和基本类型在这里的返回有一处有区别如上要注意

        执行顺序就是try-catch-finally