[Solved] What does the ‘{‘ symbol (curly-brace) indicate in Java?

Question

The question from your instructor seems not so great because there isn’t a single unified meaning of the { symbol in Java.

In the context of a statement, the { symbol is used to denote the start of a block statement. This accounts for all the uses of { with if statements, while loops, for loops, do … while loops, switch statements, etc., which technically only apply to a single statement but are often used with block statements:

if (x == 0) {
    statementOne();
    statementTwo();
}

In the context of a method or type (class/interface/enum/annotation), the { symbol is used to denote the beginning of the body of a class or a method:

public class NewClass {
    ...

    public void foo() {
         ...
    }
}

It can also be used inside a class to declare an initializer or static initializer block:

class MyClass() {
    static int x;
    static {
        x = somethingHorrible();
    }
};

In the context of an array literal, the { symbol is used to denote the beginning of the list of elements used inside that literal:

int[] arr = new int[] {1, 3, 7};

Each of these uses of the open brace symbol is different from all the others. In fact, the language would work just fine if we used a different symbol for each of these different contexts.

I think that the best answer to your question is that { is used in contexts where some group of things will be treated as a unit, whether it’s a block statement (many statements treated as a single one), a class (many methods and fields treated as a single object), a method (many statements treated as a single unified piece of code), an initializer (many things that need to be done at once), etc.

In the majority of these contexts, as the comments have pointed out, the brace introduces a new scope. Statement blocks, class bodies, initializer bodies, and function bodies all introduce a new scope, and that is definitely something important to keep in mind. (Array initialization doesn’t do this, though.)

Accepted Answer