try-catch-finally的那点事

关于try-catch-finally以及值类型和引用类型。

       finally是必须执行的，这点是毋庸置疑的。

       return之前会先执行finally里的代码，对于非对象类型，finally里的代码不能通过重新给变量赋值来改变return语句的返回值，对于对象类型，和其不同，一个为复制，一个为引用。

       也就是说，在进入finally之前，return已经将值压栈，而finally對值进行改变，并不影响值得返回，而对于引用就不一样了，压栈的是引用，返回的也是引用。

       如果return是写在finally的话，就好办了，在finally对值进行改变，然后返回，退出程序。

  JAVA CODE

 

 public class Test_try {
   
    public static void main(String[] args) {
        Test_try t=new Test_try();
        System.out.println("测试finally单纯修改返回值" + t.doPrint1());
        System.out.println("测试finally修改返回值并返回" + t.doPrint2());
        System.out.println("测试finally修改对象类型" + t.doPrint3());
        System.out.println("测试finally修改对象类型并返回" + t.doPrint4());
    }

    private int doPrint1(){
        int a = 0;
        try{
            a = 1;
            throw new SecurityException();
        }
        catch(Exception e){
            System.out.println("catch_begin");
            a = 2;
            return a;     
        }
        finally{
            a=3;
            System.out.println("finally_end" + a);
        }
    }
   
    private int doPrint2(){
        int a = 0;
        try{
            a = 1;
            throw new SecurityException();
        }
        catch(Exception e){
            System.out.println("catch_begin");
            a++;
            return a;
            }
        finally{
            a++;
            System.out.println("finally_end" + a);
            return a;
        }
    }
   
    private StringBuffer doPrint3(){
        StringBuffer a = new StringBuffer(); 
        try{
            a.append(1);
            throw new SecurityException();
        }
        catch(Exception e){
            System.out.println("catch_begin");
            a.append(1);
            return a;   
        }
        finally{
            a.append(1);
            System.out.println("finally_end" + a);
        }
    }
   
    private StringBuffer doPrint4(){
        StringBuffer a = new StringBuffer(); 
        try{
            a.append(1);
            throw new SecurityException();
        }
        catch(Exception e){
            System.out.println("catch_begin");
            a.append(1);
            return a;           
        }
        finally{
            a.append(1);
            System.out.println("finally_end" + a);
            return a;
        }
    }
}

  

============

输出结果：

catch_begin
finally_end3
测试finally单纯修改返回值2
catch_begin
finally_end3
测试finally修改返回值并返回3
catch_begin
finally_end111
测试finally修改对象类型111
catch_begin
finally_end111
测试finally修改对象类型并返回111