Java异常try{}catch{}中的return机制

try catch 和方法中都有返回

public class MainTest {
    public static void main(String[] args) {
        System.out.println("测试结果 " + test(true));
    }

    static String test(boolean exception){
        try {
            System.out.println("start");
            if(exception){
                throw new Exception(new RuntimeException());
            }
            return "try";
        } catch (Exception e){
            System.out.println("Exception");
            e.printStackTrace();
            return "Exception";
        } finally {
            System.out.println("finally");
            //return "finally";
        }
        return "test";
    }
}
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不允许这样写，运行时会报“错误: 无法访问的语句 return “test”;
当try 和catch 中都有返回时，方法是不允许有return,因为代码不会执行到try catch之外。

try 和方法中都有返回

public class MainTest {
    public static void main(String[] args) {
        System.out.println("测试结果 " + test(true));
    }

    static String test(boolean exception){
        try {
            System.out.println("start");
            if(exception){
                throw new Exception(new RuntimeException());
            }
            return "try";
        } catch (Exception e){
            System.out.println("Exception");
            e.printStackTrace();
           // return "Exception";
        } finally {
            System.out.println("finally");
            //return "finally";
        }
        System.out.println("最后一行");
        return "finish";
    }
}
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结果

start
Exception
finally
最后一行
测试结果 finish
java.lang.Exception: java.lang.RuntimeException
	at com.example.testdemo.MainTest.test(MainTest.java:12)
	at com.example.testdemo.MainTest.main(MainTest.java:5)
Caused by: java.lang.RuntimeException
	... 2 more

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1.方法执行完毕后抛出异常
2.先进入到catch中，然后是finally，最后执行方法return

finally和方法中都有return

public class MainTest {
    public static void main(String[] args) {
        System.out.println("测试结果 " + test(true));
    }

    static String test(boolean exception){
        try {
            System.out.println("start");
            if(exception){
                throw new Exception(new RuntimeException());
            }
           //return "try";
        } catch (Exception e){
            System.out.println("Exception");
            e.printStackTrace();
            //return "Exception";
        } finally {
            System.out.println("finally");
            return "finally";
        }
        System.out.println("最后一行");
        return "finish";
    }
}
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无法执行，因为finally一定会被执行，方法的return无法执行

try catch 和finally中都有return

public class MainTest {
    public static void main(String[] args) {
        System.out.println("测试结果 " + test(false));
    }

    static String test(boolean exception){
        try {
            System.out.println("start");
            if(exception){
                throw new Exception(new RuntimeException());
            }
           return "try";
        } catch (Exception e){
            System.out.println("Exception");
            e.printStackTrace();
            return "Exception";
        } finally {
            System.out.println("finally");
            return "finally";
        }
//        System.out.println("最后一行");
//        return "finish";
    }
}
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start
finally
测试结果 finally
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最终执行finally中的return