Fundamentals of Java Static Methods and Variables

Do you have any of below questions?

• Could you write down Java static methods best practices?
• What is Java static methods in interface?
• Have a question on Java static methods vs singleton?
• Java static methods vs instance methods performance
• Java static methods and variables
• Java static methods vs non static
• Java static methods in abstract class

The static keyword can be used in 3 scenarios:

• Static variables
• Static methods
• Static blocks of code.

static variable (“static” Keyword = Class Variables)

In Java Variables can be declared with the “static” keyword.

Example: static int y = 0;

When a variable is declared with the keyword static, it’s called a class variable. All instances share the same copy of the variable. A class variable can be accessed directly with the class, without the need to create a instance.

No “static” Keyword = Instance Variables

Without the static keyword, it’s called instance variable, and each instance of the class has its own copy of the variable.

Example: static int crunchify_variable_name;

• The static variables are shared among all the instances of the class.
• One of the main reason you need it when you want to do lots of memory management.
• For all static variable – there will be only one single copy available for you to use.
• You absolutely don’t need an class object in order to access static variable.
  • Just use it directly. You don’t need object.StaticVariable

What is Static block?

The static block, is a block of statement inside a Java class that will be executed when a class is first loaded into the JVM.

Can you override private method in Java?

• Well, no. Private methods can’t be override as it’s not available to use outside of class.

Why can’t we override static methods in Java?

• Static methods also can’t be overridden as it’s part of a class rather than an object

Can we access non static variable in static context?

• To be able to access non static variable from your static methods they need to be static member variables.

Details on Static method

• How to identify? Just check this first. Do you need an class object to access static method? If you don’t need an object then it’s Static method.
• You need to use static keyword in order to specify static method
• Better use keyword static if that method is not going to change throughout your project at runtime.
• You can’t override static method.

Let’s take a look at below Examples:

Example-1:

package crunchify.com.tutorials;

/**
 * @author Crunchify.com
 * 
 */

public class CrunchifyStaticMethodMain {

	public static void main(String args[]) {
		String[] crunchifyObject = new String[3];
		crunchifyObject = new String[] { "Google", "Facebook", "Crunchify" };

		// creating instnace
		CrunchifyStaticMethodMain object = new CrunchifyStaticMethodMain();
		object.crunchifyTestMethod(crunchifyObject);

	}

	/*
	 * Check this out: Let's understand little more...
	 * 
	 * Here method crunchifyTestMethod is defined as 
	 * public void crunchifyTestMethod(String[]) 
	 * so it is "non-static". It can't be called unless it is called on an instance of CrunchifyStaticMethodMain.
	 * 
	 * If you declared your method as 
	 * public static void crunchifyTestMethod(int[]) 
	 * then you could call: CrunchifyStaticMethodMain.crunchifyTestMethod(arr); within main without having created an instance for it.
	 */

	public void crunchifyTestMethod(String[] crunchifyObject) {
		for (int i = 0; i < crunchifyObject.length; i++)
			System.out.println(crunchifyObject[i]);

	}

}

Check it out the explanation in above code block. We have to create instance of Class to access non-static method.

Example-2:

package com.crunchify.tutorials;

/**
 * @author Crunchify.com
 */

public class CrunchifyStaticDeclaration {

	// 1st static block 
	static {
		System.out.println("\nI'm static block 1..");
		setTestString("This is static block's String");
		setTestValue(2);
	}

	// 2nd static blocks in same class
	static {
		System.out.println("\nI'm static block 2..");
	}

	// static variable example
	private static int testValue; // kept private to control it's value through setter

	public int getTestValue() {
		return testValue;
	}

	// static method example
	public static void setTestValue(int testValue) {
		if (testValue > 0)
			CrunchifyStaticDeclaration.testValue = testValue;
		System.out.println("setTestValue method: " + testValue);
	}

	public static String testString;

	/**
	 * @return the testString
	 */
	public static String getTestString() {
		return testString;
	}

	/**
	 * @param testString the testString to set
	 */
	public static void setTestString(String testString) {
		CrunchifyStaticDeclaration.testString = testString;
		System.out.println("setTestString method: " + testString);
	}

	// static util method
	public static int subValue(int i, int... js) {
		int sum = i;
		for (int x : js)
			sum -= x;
		return sum;
	}
}

Now let’s do test:

package com.crunchify.tutorials;

/**
 * @author Crunchify.com
 */

public class CrunchifyStaticExample {

	public static void main(String[] args) {
		CrunchifyStaticDeclaration.setTestValue(5);

		// non-private static variables can be accessed with class name
		CrunchifyStaticDeclaration.testString = "\nAssigning testString a value";
		CrunchifyStaticDeclaration csd = new CrunchifyStaticDeclaration();
		System.out.println(csd.getTestString());

		// class and instance static variables are same
		System.out.print("\nCheck if Class and Instance Static Variables are same:  ");
		System.out.println(CrunchifyStaticDeclaration.testString == csd.testString);
		System.out.println("Why? Because: CrunchifyStaticDeclaration.testString == csd.testString");
	}
}

Output:

I'm static block 1..
setTestString method: This is static block's String
setTestValue method: 2

I'm static block 2..
setTestValue method: 5

Assigning testString a value

Check if Class and Instance Static Variables are same:  true
Why? Because: CrunchifyStaticDeclaration.testString == csd.testString

The post Fundamentals of Java Static Methods and Variables appeared first on Crunchify.

Author: App Shah