return关键字在Java中的void方法中做了什么？

Question

I'm looking at a path finding tutorial and I noticed a return statement inside a void method (class PathTest , line 126):

if ((x < 0) || (y < 0) || (x >= map.getWidthInTiles()) || (y >= map.getHeightInTiles())) {
    return;
}

I'm a novice at Java. Can anyone tell me why it's there? As far as I knew, return inside a void method isn't allowed.

Answer 1

It just exits the method at that point. Once return is executed, the rest of the code won't be executed.

eg.

public void test(int n) {
    if (n == 1) {
        return; 
    }
    else if (n == 2) {
        doStuff();
        return;
    }
    doOtherStuff();
}

Note that the compiler is smart enough to tell you some code cannot be reached:

if (n == 3) {
    return;
    youWillGetAnError(); //compiler error here
}

Answer 2

You can have return in a void method, you just can't return any value (as in return 5; ), that's why they call it a void method. Some people always explicitly end void methods with a return statement, but it's not mandatory. It can be used to leave a function early, though:

void someFunct(int arg)
{
    if (arg == 0)
    {
        //Leave because this is a bad value
        return;
    }
    //Otherwise, do something
}

Answer 3

关键字只是从调用堆栈中弹出一个帧，将控件返回到函数调用之后的行。

Answer 4

Java语言规范说如果方法返回void，则可以返回没有表达式。

Answer 5

它的功能与带有指定参数的函数返回相同，但它不返回任何内容，因为没有任何内容可以返回，并且控制权被传递回调用方法。

Answer 6

It exits the function and returns nothing.

Something like return 1; would be incorrect since it returns integer 1.

Answer 7

See this example, you want to add to the list conditionally. Without the word "return", all ifs will be executed and add to the ArrayList!

    Arraylist<String> list =  new ArrayList<>();

    public void addingToTheList() {

    if(isSunday()) {
        list.add("Pray today")
        return;
    }

    if(isMonday()) {
        list.add("Work today"
        return;
    }

    if(isTuesday()) {
        list.add("Tr today")
        return;
    }
}