What's the Difference Between Static and Non-Static Initialization Code Blocks in Java?

Static vs. Non-Static Initialization Code Blocks

In Java, the static keyword can be used to declare class-level variables and methods that are accessible without creating an instance of the class. However, it is also possible to use static with code blocks that are not part of any function within the class.

Class Initialization Code Block

A class initialization code block is declared using the static modifier. It is executed when the class is loaded into memory and is used to initialize static variables and perform other class-level tasks. For example:

public class Test {
    private static int a = 5;
    static {
        System.out.println("Class initialization code executed");
    }
}

The class initialization code block will be executed before any instance of the Test class is created, and the variable a will be initialized to 5.

Instance Initialization Code Block

An instance initialization code block is declared without the static modifier and is executed when an instance of the class is created. It is used to initialize instance variables and perform other initialization tasks for the instance. For example:

public class Test {
    private int a = 5;
    {
        System.out.println("Instance initialization code executed");
    }
}

The instance initialization code block will be executed before the constructor of the Test class is called, and the variable a will be initialized to 5.

Key Differences

The key differences between class and instance initialization code blocks are as follows:

• Class initialization code blocks are executed when the class is loaded, while instance initialization code blocks are executed when an instance of the class is created.
• Class initialization code blocks can access static variables, while instance initialization code blocks can access both static and instance variables.
• Class initialization code blocks are shared among all instances of the class, while instance initialization code blocks are specific to each instance.

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