Java Tutorial: Methods in Java

• Sometimes our program grows in size, and we want to separate the logic of the main method from the other methods.
• For instance, if we calculate the average of a number pair 5 times, we can use methods to avoid repeating the logic. [DRY – Don’t Repeat Yourself]

Syntax of a Method

• A method is a function written inside a class. Since Java is an object-oriented language, we need to write the method inside some class.
• Syntax of a method :

returnType nameOfMethod() {
//Method body
}

• The following method returns the sum of two numbers

int mySum(int a, int b) {
	int c = a+b;
	return c;	//Return value
}

• In the above method, int is the return data type of the mySum function.
• mySum takes two parameters: int a and int b.
• The sum of two values integer values(a and b) is stored in another integer value named 'c'.
• mySum returns c.

Calling a Method :

• A method can be called by creating an object of the class in which the method exists followed by the method call:

Calc obj = new Calc(); //Object Creation

obj.mySum(a , b); //Method call upon an object

• The values from the method call (a and b) are copied to the a and b of the function mySum. Thus even if we modify the values a and b inside the method, the values in the main method will not change.

Void return type :

• When we don’t want our method to return anything, we use void as the return type.

Static keyword :

• The static keyword is used to associate a method of a given class with the class rather than the object.
• You can call a static method without creating an instance of the class.
• In Java, the main() method is static, so that JVM can call the main() method directly without allocating any extra memory for object creation.
• All the objects share the static method in a class.

Process of method invocation in Java :

• Consider the method Sum of the calculate class as given in the below code :

class calculate{
     int sum(int a,int b){
        return a+b;
    }

• The method is called like this:

class calculate{
     int sum(int a,int b){
        return a+b;
    }

public static void main(String[] args) {
         
        calculate obj = new calculate();
        int c = obj.sum(5,4);
        System.out.println(c);
    }
}

Output : 9

• Inside the main() method, we've created an object of the calculate class.
• obj is the name of the calculate class.
• Then, we've invoked the sum method and passed 5 and 4 as arguments.

Note: In the case of Arrays, the reference is passed. The same is the case for object passing to methods.

Code as described in the video:

package com.company;

public class cwh_31_methods {

    static int logic(int x, int y){
        int z;
        if(x>y){
            z = x+y;
        }
        else {
            z = (x +y) * 5;
        }
        x = 566;
        return z;
    }


    public static void main(String[] args) {
        int a = 5;
        int b = 7;
        int c;
        // Method invocation using Object creation
        //cwh_31_methods obj = new cwh_31_methods();
        //c = obj.logic(a, b);
        c = logic(a, b);
        System.out.println(a + " "+ b);
        int a1 = 2;
        int b1 = 1;
        int c1;
        c1 = logic(a1, b1);
        System.out.println(c);
        System.out.println(c1);
    }
}

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