static block vs static method in Java

1. Introduction

In Java, both static blocks and static methods are associated with a class rather than with instances of the class. A static block, also known as a static initialization block, is a group of statements that gets executed when the class is loaded into memory. A static method, on the other hand, is a method that belongs to the class and not to any individual object. Static methods can be called without creating an instance of the class.

2. Key Points

1. Static blocks are executed automatically when the class is loaded and cannot be called directly.

2. Static methods must be called explicitly using the class name and can be called any time after the class is loaded.

3. Static blocks are typically used for initializing static variables.

4. Static methods can have return types and can accept arguments, allowing more flexibility in their use.

3. Differences Between static block and static method in Java

Static Block	Static Method
A static block is a group of statements inside a Java class that gets executed when the class is first loaded into the JVM.	A static method is a method that belongs to the class, not to a specific instance, and can be called without creating an instance of the class.
Used for static initialization of a class. This can include initialization of static variables that require more than the default value.	Used to perform operations that don't require any data from an instance of the class (the object), but rather are global to all instances
Executes automatically when the class is loaded.	It can be called at any time after the class is loaded using the class name without needing an object of the class.
You cannot pass parameters to a static block.	You can pass parameters to static methods, just like instance methods.
If a class contains multiple static blocks, they are executed in the order they appear in the class.	Static methods can be overloaded and invoked independently, identified by their method names and parameters.
Typically used for static initialization operations that are run once per class load.	Typically used for utility functions, it can be called at any time without creating an instance of the class.

4. Example

public class StaticExample {
    static int num;
    static String myStr;

    // Static block
    static {
        num = 97;
        myStr = "Block";
        System.out.println("Static Block initialized.");
    }

    // Static method
    static void myStaticMethod() {
        System.out.println("Static Method invoked.");
        num = 123;
        myStr = "Method";
    }

    public static void main(String args[]) {
        System.out.println("Main method invoked.");
        System.out.println("Value of num: " + num);
        System.out.println("Value of myStr: " + myStr);

        // Static method call
        StaticExample.myStaticMethod();

        System.out.println("Value of num after calling myStaticMethod: " + num);
        System.out.println("Value of myStr after calling myStaticMethod: " + myStr);
    }
}

Output:

Static Block initialized.
Main method invoked.
Value of num: 97
Value of myStr: Block
Static Method invoked.
Value of num after calling myStaticMethod: 123
Value of myStr after calling myStaticMethod: Method

Explanation:

1. The static block initializes num and myStr when StaticExample class is loaded.

2. The main method is called and it prints the values of num and myStr initialized by the static block.

3. The myStaticMethod is explicitly called in the main method, which updates the values of num and myStr and prints them out.

5. When to use?

- Use static blocks when you need to initialize static variables when the class is loaded.

- Use static methods when you need to perform operations that do not require data from an instance of the class.