Java中try，return ，finally，throw使用总结

（1）       当 try 中抛出异常且 catch 中有 return 语句， finally 中没有 return 语句， java 先执行 catch 中非 return 语句，再执行 finally 语句，最后执行 catch 中 return 语句。详见情况一。

（2）       当 try 中抛出异常且 catch 中有 return 语句， finally 中也有 return 语句， java 先执行 catch 中非 return 语句，再执行 finally 中非 return 语句，最后执行 finally 中 return 语句，函数返回值为 finally 中返回的值。详见情况二。

（3）       Throw （无能是 catch 中还是非 catch 中）后面不能再跟 code ，否则编译不能通过。详见下面情况三，四，五。

Return ， finally 总结：

情况一，代码如下：

public class Test {

public int testTry(){

       FileInputStream fi=null;

      

       try{

           fi=new FileInputStream("");

          

       }catch(FileNotFoundException fnfe){

            System.out.println("this is FileNotFoundException");

            return 1;

       }catch(SecurityException se){

           System.out.println("this is SecurityException");

       }finally{

           System.out.println("this is finally");

       }

       return 0;

}

 

public static void main(String[] args) {

Test t= new Test();

       System. out .println(t.testTry());

}

}

Output ：

this is FileNotFoundException

this is finally

1

 

情况二，代码修改如下：

public class Test {

public int testTry(){

       FileInputStream fi=null;

      

       try{

           fi=new FileInputStream("");

          

       }catch(FileNotFoundException fnfe){

            System.out.println("this is FileNotFoundException");

            return 1;

       }catch(SecurityException se){

           System.out.println("this is SecurityException");

       }finally{

           System.out.println("this is finally");

             return 3;

       }

       //return 0;

}

 

public static void main(String[] args) {

Test t= new Test();

       System. out .println(t.testTry());

}

}

Output ：

this is FileNotFoundException

this is finally

3

----------------------------------------------------

Return throw 总结：

情况三：

public class Test {

    public static void main(String[] args) {

       Test t=new Test();

       try{

       System.out.println(t.testTry());

       }catch(Exception e){

           System.out.println("this is exception");

       }

      

    }

    public int testTry()throws Exception{

       FileInputStream fi=null;

      

       try{

           fi=new FileInputStream("");

          

       }catch(FileNotFoundException fnfe){

            //System.out.println("this is FileNotFoundException"); 

           throw new Exception();

           return 1;

       }catch(SecurityException se){

           System.out.println("this is SecurityException");

       }finally{

           System.out.println("this is finally");

       }

       return 0;

    }

}

 

>javac Test.java

Test.java:22: 无法访问的语句

                     Return 1;

 

情况四：

public class Test {

    public static void main(String[] args) {

       Test t=new Test();

       try{

       System.out.println(t.testTry());

       }catch(Exception e){

           System.out.println("this is exception");

       }

      

    }

    public int testTry()throws Exception{

       FileInputStream fi=null;

      

       try{

           fi=new FileInputStream("");

          

       }catch(FileNotFoundException fnfe){

            //System.out.println("this is FileNotFoundException"); 

           throw new Exception();

           System.out.println("after throw exception");

          // return 1;

       }catch(SecurityException se){

           System.out.println("this is SecurityException");

       }finally{

           System.out.println("this is finally");

       }

       return 0;

    }

}

>javac Test.java

Test.java:22: 无法访问的语句

                     System.out.println("this is SecurityException");

 

情况五：

public class Test {

    public static void main(String[] args) {

       Test t=new Test();

       try{

       t.testTry();

       }catch(Exception e){

           System.out.println("this is exception");

       }

      

    }

    public void testTry()throws Exception{

       throw new Exception();

       System.out.println("this is testTry method");

    }

}

>javac Test.java

Test.java:22: 无法访问的语句

                    System.out.println("this is testTry method");

 

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