using parenthesis in declaration of variable

Question

When & Why parenthesis are used in declaring a variable.For example :

 Graphics2D g2 = (Graphics2D)g;

Here why Graphics2D are put in Parenthesis and what is the use of these ().

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@namanjain casting converts one object type to another (if possible). — ryrich, Mar 28 '14 at 13:39
@ryrich Casting isn't conversion, and it's important not to confuse the two. — chrylis -cautiouslyoptimistic-, Mar 28 '14 at 13:47
possible duplicate of [Casting objects in Java](http://stackoverflow.com/questions/5306835/casting-objects-in-java) — Alexis Leclerc, Mar 28 '14 at 13:51
@chrylis I'm pretty sure we could argue semantics all day, but what I said is true. Casting is also known as type conversion. Please check out the docs! http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html — ryrich, Mar 28 '14 at 13:54

score 4 · Accepted Answer · answered Mar 28 '14 at 13:40

4

This is a cast. You are casting the g object (of type graphics) to a more specific type of Graphics2D

As per the document:

This Graphics2D class extends the Graphics class to provide more sophisticated control over geometry, coordinate transformations, color management, and text layout. This is the fundamental class for rendering 2-dimensional shapes, text and images on the Java(tm) platform.

Basically you are telling your code to take the g object and treat it like a graphics2d object which has more features. You can do this because Graphics2D is a "subclass" of graphics.

answered Mar 28 '14 at 13:40

Jeef

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So in parenthesis we used the type to which we want to convert the object – cool joey Mar 28 '14 at 13:43
@namanjain It's not converting; it's telling the compiler that you expect that the object is really a subclass of its declared type. If it's not already the type you try to cast it to, you'll get a `ClassCastException`. – chrylis -cautiouslyoptimistic- Mar 28 '14 at 13:46
@chrylis - well said! – Jeef Mar 28 '14 at 18:45

score 1 · Answer 2 · answered Mar 28 '14 at 13:51

It's used to cast from one type to another one.

Ex:

float floatingNumber = 5.2;
int integerNumber = (int) floatingNumber;

In this case, the (int) takes just the integer part from the floating point number stored on "floatingNumber". So integerNumber will now store the value 5, which is the integer part of floatingNumber.

using parenthesis in declaration of variable

2 Answers2