Shulou(Shulou.com)06/02 Report--

This article will explain in detail about the impact of the Final keyword on the JVM class loader, the content of the article is of high quality, so the editor will share it for you to do a reference. I hope you will have a certain understanding of the relevant knowledge after reading this article.

When a class has a variable declared as static final, and such a variable has an impact on the class loader, first take a look at the following example.

Package com.bird.classLoad; class FinalTest {public static final int a = 6 System.out.println 3; static {System.out.println ("FinalTest static block");}} public class Test3 {public static void main (String [] args) {System.out.println (FinalTest.a);}}

Because an is a static final variable and it equals 6 FinalTest 3, its value is known at compile time, so direct access to the value of a does not cause initialization of the class. As a manifestation, the static static code will not be loaded quickly.

The running result is

two

Looking at an example.

Package com.bird.classLoad; import java.util.Random; class FinalTest4 {public static final int a = new Random (). NextInt; static {System.out.println ("FinalTest4 static block");} public class Test4 {public static void main (String [] args) {System.out.println (FinalTest4.a);}}

This static final variable a can't be known until run time because I cannot know its exact value at compile time, so accessing FinalTest4.an itself will cause the initialization of the FinalTest4 class. That is, static static code loads quickly.

The running result is

FinalTest4 static block 82

The following example shows that when a subclass is actively accessed, it causes initialization of its immediate parent class.

Package com.bird.classLoad; class Parent {static int a = 3; static {System.out.println ("Parent static block");} class Child extends Parent {static int b = 4; static {System.out.println ("Chind static block") }} public class Test5 {public static void main (String [] args) {System.out.println (Child.b);}}

Because of direct access to Child,b, the Parent class is initialized first, followed by the Child class.

The running result is

Parent static block Chind static block 4

If you access the variables of the parent class directly through the subclass, only the parent class will be initialized, not the subclass

Package com.bird.classLoad; class Parent {static int a = 3; static {System.out.println ("Parent static block");}} class Child extends Parent {static {System.out.println ("Chind static block");}} public class Test5 {public static void main (String [] args) {System.out.println (Child.a) }}

If you directly access the a variable of the Parent class, only the parent class will be initialized, not the Child class.

The running result is as follows

Parent static block 3 about the impact of the Final keyword on the JVM class loader is shared here, I hope the above content can be of some help to you, can learn more knowledge. If you think the article is good, you can share it for more people to see.

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