What ARE appropriate uses of final and static

[Matt Kohanek]

In school and in any subsequent tutorials I have read through, the instances in which you should not use final and static are given. However, I have never really seen or been given an example of when using these keywords is appropriate. In all my programs I have never really needed them either.

Can anyone give me a real example of when they are useful and/or necessary?

[fred rosenberger]

You can use 'final' when you don't want the value of a variable to change once it is set.

Static is used when you want to be able to reference the variable without creating an instance of the class.

for example, in the Math class, there is a variable called PI. It is final, because you don't want anyone to be able to change it. It is static, because there is no reason to force someone to create an instance of the Math class just to get the value - the value can exist regardless.

[David Newton]

The final keyword can also be used to express intent. Some people declare all parameters as final to avoid accidental (or purposeful) reuse in a method body. Some people declare some or all local variables as final, again to express intent.

Finally, variables must be final if they're going to be used by an anonymous inner class.

[Jesper de Jong]

It's a good idea to make classes final unless they are designed to be extended by subclasses: see Item 17 ("Design and document for inheritance or else prohibit it") in the book Effective Java (highly recommended if you want to become a better Java programmer!).

Also, I prefer to make classes immutable because it has a number of advantages (you don't need to make defensive copies, they are thread-safe etc.). For example, instead of writing a simple class like this:

// Mutable Person class
public class Person {
	private String name;
	private int age;

	public Person(String name, int age) {
		this.name = name;
		this.age = age;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}
}

I prefer to write it like this:

// Immutable Person class
public final class Person {
	private final String name;
	private final int age;

	public Person(String name, int age) {
		this.name = name;
		this.age = age;
	}

	public String getName() {
		return name;
	}

	public int getAge() {
		return age;
	}
}

[Rahul Nair]

Hi,

The Final keyword is one of the useful keyword in class design. Some classes in java language is marked final e.g. String, Wrapper Classes, StringBuffer, etc. Obviously, sometimes there is no need to extend classes in our application. e.g. String in java provide some machine level implementation(String memory pool) for creating objects of string, so in that case user don't need to extend the class. And Class Designer also don't want it so... They have marked class as final.

Static keyword is used for class level implementation of Variables/Methods and not for Object level. So for this purpose we can access the variable using the directly the Class Name and not an object of the class, Though you have mentioned "object.methodName()" for calling the static method then also internally it will consider it as "ClassName.methodeName()". As obvious it will also get rid of unnecessary objects that we have to create for calling the methods which we can mark as static.

Ranchers please correct me if i am wrong somewhere...

Thanks,

Rahul

[Campbell Ritchie]

The final keyword has different effects depending on whether it is applied to a class, a method or a field/variable.

[Jim Hoglund]

Your question about the appropriate uses of 'static' and 'final' is a little like
asking about the appropriate uses of a hammer or a shovel. 'static' and 'final'
are very powerful general purpose Java tools. So beyond saying, "Use them to
pound on something, or to dig at something," trying to list (and memorize) good
uses can be an endless task.

A better approach is to gain a full understanding of these Java concepts, in part by
studying examples, of course. You will then be able to recognize design situations
where 'static' and 'final' should be applied.

Jim ... ...

[Thanigai arasu Ruthirakotti]

The final is the powerful keywords in java for class design.

While design your application, The class that you don't want to inherit then define as the final class. Mostly the Util classes should be the final class. String is one of the final class in java. If you want the method should not be over-ridden, then the method should be final. If you want to declare the variable to treat like constant, then it should be final variable.

Static keyword is used for class level implementation of Variables/Methods and not for Object level. The intention here is to access the variable using the directly the Class Name. Same time, if you mentioned object.methodName() or object.variableName for calling the static method then also internally it will consider it as ClassName.methodeName().

[Matt Kohanek]

Ha, it is funny to see a reply notification email show up for something I posted 4 years ago. I have been a developer for 4 1/2 years now, and I definitely know the uses of final and static at this point.
It is kind of funny, and actually pretty embarrassing to look back and see my past self ask these types of questions now

[Campbell Ritchie]

We were all at that stage once, so there is no need to be embarrassed.

[Liutauras Vilda]

Matt Kohanek wrote:Ha, it is funny to see a reply notification email show up for something I posted 4 years ago. I have been a developer for 4 1/2 years now, and I definitely know the uses of final and static at this point.
It is kind of funny, and actually pretty embarrassing to look back and see my past self ask these types of questions now

In order to stop notifications about the post you're not interested anymore, press button "Stop Watching".

[Tony Docherty]

Matt Kohanek wrote:Ha, it is funny to see a reply notification email show up for something I posted 4 years ago. I have been a developer for 4 1/2 years now, and I definitely know the uses of final and static at this point.
It is kind of funny, and actually pretty embarrassing to look back and see my past self ask these types of questions now

The other way to look at it is wow haven't I learn't a lot in the last 4 years.

[Paweł Baczyński]

David Newton wrote:Finally, variables must be final if they're going to be used by an anonymous inner class.

Beginning with Java 8 this statement is no longer true. ;)