java difference between system.out.println() and println()

问题

I was wondering if there was a difference between these two e.g.

System.out.println("Hello World");

and

println("Hello World");

I know they print the same thing, but is there anything different? (I'm new to java, so I don't know so far)

In other words, does the "System.out" change anything?

回答1:

Yes, there is a difference, because they are not calling the same method.

Assuming the second statement actually compile, it means that the println("Hello World") call is for a method that is either:

• defined in your class
• inherited from a super class
• a default method inherited from an interface (Java 8+)
• statically imported¹

Now, the local/inherited/imported println(String s) method could just have been implemented to call System.out.println(s), which would make it behave the same as the direct call to System.out.println(s), but that's different.

---

^{1) Since you cannot statically import java.lang.System.out.println() (it is not a static method), it would have to be statically imported from some other class.}

回答2:

You might have a local method called println or a static import. So:

private void println(String str) {
    //
}

or

import static java.lang.System.out;

but then it'd have to be:

out.println("bla bla");

If you are using an IDE, try to open its declaration (F3 in Eclipse) and see where it takes you.

来源：https://stackoverflow.com/questions/37871663/java-difference-between-system-out-println-and-println