003-try-catch-finally-return执行顺序问题

一、try-catch-finally-return执行顺序问题

0、原始执行顺序

try — > finally

try —> catch —> finally

1、try catch 中有 return，finally 中无 return，且 try 中无异常抛出

public int add(){
    int i = 1;
    try{
        i = i + 1;
        System.out.println("try: i = " + i);
        return i;
    }catch (Exception e){
        i = i + 2;
        System.out.println("exception: i = " + i);
        return i;
    }finally {
        i = i + 3;
        System.out.println("finally: i = " + i);
    }
}
/**
执行结果：
try: i = 2
finally: i = 5
2
*/

2、try catch finally中均有 return，try中无异常抛出

public int add(){
    int i = 1;
    try{
        i = i + 1;
        System.out.println("try: i = " + i);
        return i;
    }catch (Exception e){
        i = i + 2;
        System.out.println("exception: i = " + i);
        return i;
    }finally {
        i = i + 3;
        System.out.println("finally: i = " + i);
        return i;
    }
}
/**
返回结果5
try: i = 2
finally: i = 5
5
*/

3、try catch 中有 return，finally 中无 return，且 try 中有异常抛出

public int add(){
    int i = 1;
    try{
        i = i + 1;
        int a = i/0;
        System.out.println("try: i = " + i);
        return i;
    }catch (Exception e){
        i = i + 2;
        System.out.println("exception: i = " + i);
        return i;
    }finally {
        i = i + 3;
        System.out.println("finally: i = " + i);
    }
}
/**
返回结果4
exception: i = 4
finally: i = 7
4
*/

4、try catch finally中均有 return，try中有异常抛出

public int add(){
    int i = 1;
    try{
        i = i + 1;
        int a = i/0;
        System.out.println("try: i = " + i);
        return i;
    }catch (Exception e){
        i = i + 2;
        System.out.println("exception: i = " + i);
        return i;
    }finally {
        i = i + 3;
        System.out.println("finally: i = " + i);
        return i;
    }
}
/**
返回结果5
exception: i = 4
finally: i = 7
7
*/

5、try、catch 中有 return，try finally 中有异常，finally 中的异常有 return

public int add(){
    int i = 1;
    try{
        i = i + 1;
        int a = i/0;
        System.out.println("try: i = " + i);
        return i;
    }catch (Exception e){
        i = i + 2;
        System.out.println("exception: i = " + i);
        return i;
    }finally {
        i = i + 3;
        try {
            int b = i/0;
        } catch (Exception e) {
             i = i + 5;
             return i;
        }
        System.out.println("finally: i = " + i);
    }
}
/**
exception: i = 4
12
*/

6、try、catch 中有 return，try finally 中有异常，finally 中的异常无 return

public int add(){
    int i = 1;
    try{
        i = i + 1;
        int a = i/0;
        System.out.println("try: i = " + i);
        return i;
    }catch (Exception e){
        i = i + 2;
        System.out.println("exception: i = " + i);
        return i;
    }finally {
        i = i + 3;
        try {
            int b = i/0;
        } catch (Exception e) {
             i = i + 5;
        }
        System.out.println("finally: i = " + i);
    }
}
/**
exception: i = 4
finally: i = 12
4
*/

总结

• finally 的代码总会被执行
• try、catch 中有 return 的时候，也会执行 finally。return 的时候，要注意返回值是否会受到 finally 中代码的影响。
• finally 中有 return 的时候，会直接在 finally 中退出，导致 try、catch中的 return 失效。
• finally 中如果有异常的时候，且存在 return 的时候，catch 的 return 会被覆盖。