Java异常处理场景中不同位置的返回值详细解析

Java 异常处理中的返回值在不同位置不同场景下是有一些差别的，这里需要格外注意

具体分以下两种场景：

• 1 finally语句块没有return语句，即当代码执行到try或者catch语句块中的return语句时，相当于在本地保存了一份此时返回值的变量的值副本，然后按照try catch finally的运行机制去执行finally语句块，然后回过来将刚刚保存的副本数据返回

第一个例子为在try中没有异常，直接走到try语句块中的return场景

public class Test01 {
    public static void main(String[] args) {
        int results=new Test01().test(10,2);
        System.out.println("func results:"+results);
    }

    public int test(int a,int b)
    {
        int results=0;
        try
        {
            System.out.println("in try.....");
            results+=1;
            System.out.println("results = "+results);
            return results;
        }
        catch (Exception e)
        {
            System.out.println("in catch......");
            results+=1;
            System.out.println("results = "+results);
            return results;
        }
        finally {
            System.out.println("in finally");
            results+=1;
            System.out.println("results = "+results);
        }
    }
}

执行结果如下，最后函数返回的值是1，而不是2

in try.....
results = 1
in finally
results = 2
func results:1

第二个例子为try中出现了异常，但是在catch中走到了return语句

public class Test01 {
    public static void main(String[] args) {
        int results=new Test01().test(10,2);
        System.out.println("func results:"+results);
    }

    public int test(int a,int b)
    {
        int results=0;
        try
        {
            System.out.println("in try.....");
            results+=1;
            System.out.println("results = "+results);
            double d=1/0;
            return results;
        }
        catch (Exception e)
        {
            System.out.println("in catch......");
            results+=1;
            System.out.println("results = "+results);
            return results;
        }
        finally {
            System.out.println("in finally");
            results+=1;
            System.out.println("results = "+results);
        }
    }
}

返回值如下，即此时返回值是2而不是3

in try.....
results = 1
in catch......
results = 2
in finally
results = 3
func results:2

• 2 finally语句块有return语句，此时即最终返回finally语句块中的的值，而try或者catch语句块中及时有return语句，也不会发生作用

下面的例子即try中能走到return语句，同样finally中也有return语句时候，此时返回finally语句块中的return的值

public class Test01 {
    public static void main(String[] args) {
        int results=new Test01().test(10,2);
        System.out.println("func results:"+results);
    }

    public int test(int a,int b)
    {
        int results=0;
        try
        {
            System.out.println("in try.....");
            results+=1;
            System.out.println("results = "+results);
            return results;
        }
        catch (Exception e)
        {
            System.out.println("in catch......");
            results+=1;
            System.out.println("results = "+results);
            return results;
        }
        finally {
            System.out.println("in finally");
            results+=1;
            System.out.println("results = "+results);
            return results;
        }
    }
}

执行结果如下，返回2，此时不是返回1了

in try.....
results = 1
in finally
results = 2
func results:2

下面的例子即在catch走到了return语句，同样在finally语句块中也走到了return语句，此时同样也是返回finally语句块中的值，catch语句块中的返回值失效

public class Test01 {
    public static void main(String[] args) {
        int results=new Test01().test(10,2);
        System.out.println("func results:"+results);
    }

    public int test(int a,int b)
    {
        int results=0;
        try
        {
            System.out.println("in try.....");
            results+=1;
            System.out.println("results = "+results);
            double d=1/0;
            return results;
        }
        catch (Exception e)
        {
            System.out.println("in catch......");
            results+=1;
            System.out.println("results = "+results);
            return results;
        }
        finally {
            System.out.println("in finally");
            results+=1;
            System.out.println("results = "+results);
            return results;
        }
    }
}

执行结果如下：返回3而不是2了

in try.....
results = 1
in catch......
results = 2
in finally
results = 3
func results:3