编译器不会抱怨返回类型。 为什么？

Question

I wrote the following java code, and i expected the compiler would complain about it. but i didn't get any errors. Why is this ?

    public static void main(String[] args) {
        Ba ba = new Ba();

        ba.fetchSomeValues();

    }

    public String fetchSomeValues(){
        return "Hello";     
    }

}

I am calling the method fetchSomeValues() which should return "Hello" (which is a string), and in the main method i have included ba.fetchSomeValues(); without initializing it to a String variable. The compiler doesn't complain Why is this ?

Answer 1

You don't have to assign return values to variables. You don't have to do anything at all with them.

Although it is usually not recommended to just drop some return value of a method.

A counter example might be the Map 's put method which returns the previous value associated with the key. If you don't care whether there was a previous value or not you just simply ignore the return value.

Map<Integer, String> map = new HashMap<Integer, String>();
test.put(1, "one"); // we don't assign the return value since we don't care

So in a nutshell the compiler cannot tell whether you care about return values or not. It is only a problem if the value is significant in the context you are using the method and you ignore it .

Answer 2

忽略方法的返回值绝对有效（尽管不总是建议）。

Answer 3

在Java中，您可以忽略刚发现的返回值。

Answer 4

This behavior is not specific to Java, it is in fact the norm for all the mainstream (and even those less so) languages of today. Even in FP-languages, where the focus is on side-effect-free functions whose only point is the return value, this is allowed.

You should really ask yourself, Do I want to use a language that forces me to assign every return value? Would that be a convenient language to use?

Answer 5

ba.fetchSomeValues(); does return the string "Hello" , but since you ain't got any left var (for example String s = ba.fetchSomeValues(); ), the object of string, that has the "Hello" value, created in the fetchSomeValues() method, just get unused .

Answer 6

There's nothing wrong in this code. fetchSomeValues() returns a string but you don't have to assign the value. Normally you can write String returnedValue = a.fetchSomeValues() but it is not necessary