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Final Key Word in Java

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In this tutorial you will learn about final key word of java and its different uses with fields, methods, classes

Final key word in java

In java final is a key word used in several different contexts. It is used before a variable, method, and classes so that they cannot be changed latter.

Final Variables/fields

A final variable can only once assigned a value. This value cannot be changed latter. If final variable used in class then it must assigned a value in class constructor. Attempting to change the value of final variable/field will generate error.

Example-

public class FinalField {

	public final int fistField;
	public final int secondField;

	FinalField(int first, int second) {
		fistField = first;
		secondField = second;
	}

	 [...]
}
Final Method
A final method cannot be overridden by sub class. To declare a final method put the final after the access pacifier and before the return type.
Eaxample-
public class FinalField {
			public final int addNumber(){
			final int result; 
			// Your code
			return result;
			}
		}

Final Class

A class declared final cannot be sub classed. Other classes cannot extend final class. It provides some benefit to security and thread safety.

Example-

final class MyFinalClass {
	public final int fistField;
	public final int secondField;

	MyFinalClass(int first, int second) {
		fistField = first;
		secondField = second;
	}
}

Blank Final

A blank final is a final variable introduced in java 1.1, its declaration lacks an initializer. A blank final can only be assigned to once and it must be definitely unassigned when assignment occurs. Java compiler runs a flow analysis to ensure every assignment to blank final variable. This variable must be unassigned before assignment otherwise the compiler will give an error message.

Example-

private final int j; // Declaring Blank final
	j = 5; // Initialize blank final

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Posted on: April 14, 2006 If you enjoyed this post then why not add us on Google+? Add us to your Circles

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