Initializing final member variables in Java

When you modify any variable declaration with final, you tell to compiler that once variable is initialized, its value cannot be changed.In other words, any further assignment of value is invalid attempt.
While declaring variable as final , compiler also does some bytecode optimization as you might  have guessed they going to have only one value while complete execution of program.

In this post i am going to show initialization of the final member variables. As they declared as the top level variable, so you have options of initializing in various constructs   .

Initializing final instance variable 

You can initialize the final instance variable in only in the one of following constructs.

• Initializer expression
  Its value is initialized while declaration, by evaluating its expression on right hand side as shown in following code snippet

  	public class FinalVariable {
  	// in the instance initializer expression, or while declaration itself
  	// final <type> <variable_name> = <initializer expression>;
  	final int finalInstanceField = 5;
  	}

  view raw FinalVariable.java hosted with ❤ by GitHub
• Instance initializer block
  You can assign a variable a value in its instance initializer block as shown in following code snippet

  	public class FinalVariable {
  	final int finalInstanceField;
  	{
  	// Initialization in instance initializer block
  	finalInstanceField = 5;
  	}
  	}

  view raw FinalVariable.java hosted with ❤ by GitHub
• Constructor block
  Finally in the constructor block as shown in following code snippet

  	public class FinalVariable {
  	final int finalInstanceField ;
  	public FinalVariable() {
  	// constructor
  	finalInstanceField = 7;
  	}
  	}

  view raw FinalVariable.java hosted with ❤ by GitHub

Initializing final static variable

When declare static member variable as final then in following constructs, you can  initialize

• Initializer expression
  While declaring variable, you can initialize value evaluated in initializer expression as shown following code snippet

  	public class FinalVariable {
  	// in the instance initializer expression, or while declaration itself
  	// final <type> <variable_name> = <initializer expression>;
  	static final int finalStaticField = 25;
  	}

  view raw FinalVariable.java hosted with ❤ by GitHub
• Static initializer block
  The variable can be initialized in static initializer block. Following code snippet shows initialization.

  	public class FinalVariable {
  	static final int finalStaticField;
  	static {
  	finalStaticField = 7;
  	}
  	}

  view raw FinalVariable.java hosted with ❤ by GitHub
  While initializing this final variable make sure that you are initializing only in one of the constructs, otherwise compiler throw an error.