What does the return keyword do in a void method in Java?

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.

220780 次浏览

小开

最佳答案

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
}

小开

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
}

小开

The Java language specification says you can have return with no expression if your method returns void.

小开

It functions the same as a return for function with a specified parameter, except it returns nothing, as there is nothing to return and control is passed back to the calling method.

小开

It exits the function and returns nothing.

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

小开

The keyword simply pops a frame from the call stack returning the control to the line following the function call.

小开

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;
}
}