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What is the application of final in java? I believe many inexperienced people don't know what to do about it. Therefore, this paper summarizes the causes and solutions of the problem. Through this article, I hope you can solve this problem.

Final is not commonly used in java, but it provides us with functions such as defining constants in C language, not only that, final also allows you to control whether your members, methods, or a class can be overwritten or continued, these features make final have an indispensable position in Java, and it is also one of the key words that must be known and grasped when learning Java.

Final member

When you define a variable in a class, add the final keyword in front of it, that is, once the variable is initialized, it is immutable, which means that its value is immutable for the base type, and its reference is immutable for the object variable. It can be initialized in two places, one at its definition, that is, directly assigning a value to the final variable when it is defined, and the other in the constructor. You can only choose one of these two places, either at the time of definition or in the constructor, not both at the time of definition and another value in the constructor at the same time. The following code demonstrates this:

Import java.util.List;import java.util.ArrayList;import java.util.LinkedList;public class Bat {final PI=3.14; / / gives the address value final int i; / / when it is defined, so the value final List list; / / cannot be given here because it is initialized in the constructor. This variable is also the same as above. Bat () {iposit listener new LinkedList ();} Bat (int ii,List l) {iposit listener } public static void main (String [] args) {Bat b=new Bat (); b.list.add (new Bat ()); / / b.listingnew ArrayList (); System.out.PRintln ("I =" + b.i+ "List Type:" + b.list.getClass ()); b=new Bat (23New ArrayList ()); b.list.add (new Bat ()); System.out.println ("I =" + b.i+ "List Type:" + b.list.getClass ());}}

This program simply demonstrates the general use of final. The method of initialization in the constructor is used here, which gives you a little flexibility. As shown in the two overloaded constructors of Bat, the first default constructor provides you with the default value, and the overloaded constructor initializes the final variable based on the value or type you provide. However, sometimes you don't need this flexibility, you just need to give its value at the time of definition and never change, so don't use this method again. There are two lines of statements in the main method that are commented out, and if you uncomment, the program cannot be compiled, that is, whether it is the value of I or the type of list, once initialized, it really cannot be changed. However, b can reinitialize to specify the value of I or the type of list, as shown in the output:

I have 100 List Type:class java.util.LinkedListI=23 List Type:class java.util.ArrayList

Another use is to define the parameter in the method as final, which does not make any practical sense for variables of the basic type, because the variable of the basic type passes the value when the method is called, that is, you can change the parameter variable in the method without affecting the calling statement, but it is useful for object variables, because object variables pass their references when they are passed. In this way, your changes to the object variables in the method will also affect the object variables in the calling statement. When you do not need to change the object variables as parameters in the method, explicitly use final to declare, which will prevent you from inadvertently modifying and affecting the calling method.

In addition, when the inner class in the method uses the parameter in the method, the parameter must also be declared as final before it can be used, as shown in the following code:

Public class INClass {void innerClass (final String str) {class IClass {IClass () {System.out.println (str);}} IClass ic=new IClass ();} public static void main (String [] args) {INClass inc=new INClass (); inc.innerClass ("Hello");}}

Final method

Declare the method as final, which means you already know that the function provided by this method has met your requirements, does not need to be extended, and does not allow any continued classes from this class to override the method, but you can still continue the method, that is to say, you can use it directly. In addition, there is a mechanism called inline, which allows you to insert the method body directly into the call place when you call the final method, instead of making routine method calls, such as saving breakpoints, stacking, etc., which may improve your program efficiency, but when your method body is very large, or when you call this method in multiple places, then your calling body code will expand rapidly It may affect efficiency, so you should be careful to use final method definition.

Final class

When you use final on a class, you need to think carefully, because a final class cannot be continued by anyone, which means that this class is a leaf class in a continuation tree, and the design of this class is considered perfect and does not need to be modified or extended. For members in the final class, you can define them as final or not final. As for the method, it naturally becomes the final type because the class it belongs to is final. You can also explicitly add a final to a method in the final class, but this obviously doesn't make sense.

The following program demonstrates the use of the final method and the final class:

Final class final {final String str= "final Data"; public String str1= "non final data"; final public void print () {System.out.println ("final method.");} public void what () {System.out.println (str+ "\ n" + str1);}} public class FinalDemo {/ / extends final cannot continue public static void main (String [] args) {final f=new final (); f.what (); f.print ();}

As can be seen from the program, the use of the final class is almost the same as that of the ordinary class, except that it loses its continued feature. The difference between the final method and the non-final method is also difficult to see from the program line, just remember to use it with caution.

Application of final in Design pattern

In the design pattern, there is a pattern called the invariant pattern, which can be easily implemented through the final keyword in Java. The program Bat.java used to explain the final members is an example of the invariant pattern.

So far, the use of this,static,super and final has been said, if you can roughly tell the difference and usage of these four key words, it means that you have basically mastered it. However, everything in the world is not perfect. Java provides these four key words, which brings great convenience to programmers, but it does not mean that you should use them everywhere. Once the program is abused, it will be counterproductive, so please consider it carefully when using it.

After reading the above, have you mastered the application of final in java? If you want to learn more skills or want to know more about it, you are welcome to follow the industry information channel, thank you for reading!

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