What Do Curly Braces in Java Mean by Themselves

What do curly braces in Java mean by themselves?

The only purpose of the extra braces is to provide scope-limit. The List<PExp> copy will only exist within those braces, and will have no scope outside of them.

If this is generated code, I assume the code-generator does this so it can insert some code (such as this) without having to worry about how many times it has inserted a List<PExp> copy and without having to worry about possibly renaming the variables if this snippet is inserted into the same method more than once.

What do curly braces after a 'new' statement do?

These curly braces define an anonymous inner class.

This allows you to be able to override public and protected methods of the class you are initiating. You can do this with any non-final class, but is most useful with abstract classes and interfaces, which can only be initiated this way.

(To qualify that last sentence, interfaces with only one non-default method can be initiated using lambda statements in Java 8, circumventing this design method.)

What does the '{' symbol (curly-brace) indicate in Java?

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.)

java just curly braces

It's a code block. The variables declared in there are not visible in the upper block (method body outside of these curlies), i.e. they have a more limited scope.

Generate colors between red and green for a power meter?

This should work - just linearly scale the red and green values. Assuming your max red/green/blue value is 255, and n is in range 0 .. 100

R = (255 * n) / 100
G = (255 * (100 - n)) / 100 
B = 0

(Amended for integer maths, tip of the hat to Ferrucio)

Another way to do would be to use a HSV colour model, and cycle the hue from 0 degrees (red) to 120 degrees (green) with whatever saturation and value suited you. This should give a more pleasing gradient.

Here's a demonstration of each technique - top gradient uses RGB, bottom uses HSV:

Placing arbitrary braces as statements - what do they mean?

The curly braces just create a local block scope inside your main method. The variables declared inside a block will not be visible outside.

This way of coding is used to minimize the scope of local variables.

public void someMethod() {
    {
        int x = 10;
        System.out.println(x); // Ok
    }
    System.out.println(x); // Error, x not visible here
}

It is a good practice to minimize the scope of the local variables you create, specially when you know they won't be used anywhere else in your program. So, it doesn't make sense to let it in the larger scope till it ends. Just create a local block scope, so that it will be eligible for Garbage Collection as soon as the block ends.

Also see @Bohemian's answer below that also quotes one more benefit.

Why do Java array declarations use curly brackets?

Curly brackets usually denotes sets and ensembles while parenthesis usually denotes parameters in C-like languages.

A long time ago, people got used to having this kind of convention with C. I'm pretty sure that it works this way in Java to keep some kind of syntax consistency with older languages.

What does ${} (dollar sign and curly braces) mean in a string in JavaScript?

You're talking about template literals.

They allow for both multiline strings and string interpolation.

Multiline strings:

console.log(`foobar`);// foo// bar

What does static succeeded only by two curly brackets means?

It is a static initializer block, which is used to initialize static members of the class. It is executed when the class is initialized.

Your example :

static {            
    int i1=0;
    String s1="abc";
    double d1=0;
};

makes no sense, since it declares variables that are only in scope until the execution of that block is done.

A more meaningful static initializer block would be :

static int i1;
static String s1;
static double d1; 

static {            
    i1=0;
    s1="abc";
    d1=0;
};

This example still doesn't justify using a static initializer, since you can simply initialize those static variable when you declare them. The static initializer block makes sense when the initialization of static variables is more complex.

Why is this Java code in curly braces ({}) outside of a method?

Borrowed from here -

Normally, you would put code to initialize an instance variable in a
constructor. There are two alternatives to using a constructor to
initialize instance variables: initializer blocks and final methods.
Initializer blocks for instance variables look just like static
initializer blocks, but without the static keyword:

{
    // whatever code is needed for initialization goes here
} 

The Java compiler copies initializer blocks into every constructor. Therefore, this approach can be used to share a block of code between multiple constructors.

You may also wanna look at the discussions here.

---

Related Topics