Static vs Instance Initializer Block in Java

Static vs. Instance Initializer Block in Java

Java offers two kinds of initialization blocks: static initializers and instance initializers. The difference between them is subtle but important. Knowing the appropriate use of each type of initialization block can be key to writing good, efficient code.

Static Initializer Blocks

A static initializer block is used to initialize static variables, and it is executed only once in a class’s lifetime. It is executed before the main method, and it runs when the class is first loaded. A static initializer block is a block of code surrounded by braces and preceded by the static keyword, as shown below:

static {
    // code that will be executed once 
    // when the class is first loaded
}

The code in a static initializer block must be valid Java syntax and can include assignments, method calls, or other code. A static initializer block is useful for initialization of static variables because the values can be different from one instance of a class or program run to the next.

Instance Initializer Blocks

Instance initializer blocks are used to initialize instance variables and are executed each time an instance of a class is created. An instance initializer block is a block of code surrounded by braces, but it does not require the static keyword, as shown below:

{
    // code that will be executed each time 
    // an instance of the class is created
}

The code in an instance initializer block must also be valid Java syntax and can include assignments, method calls, or other code. An instance initializer block is useful for initialization of instance variables because the values can be different for each instance of the class.

Conclusion

Static and instance initializer blocks are both useful for initialization in Java, and knowing when to use each type of block can help you write more efficient code. By using static and instance initializer blocks, you can ensure that your variables are initialized properly and that the correct values will be used.