How do I use the “return” keyword in Java?

The return keyword is used to return from a method when its execution is complete. When a return statement is reached in a method, the program returns to the code that invoked it.

A method can return a value or reference type or does not return a value. If a method does not return a value, the method must be declared void and it doesn’t need to contain a return statement.

If a method declare to return a value, then it must use the return statement within the body of method. The data type of the return value must match the method’s declared return type.

package org.kodejava.example.fundamental;

public class ReturnDemo {

    public static void main(String[] args) {
        int z = ReturnDemo.calculate(2, 3);
        System.out.println("z = " + z);

        Dog dog = new Dog("Spaniel", "Doggie");
        System.out.println(dog.getDog());
    }

    public static int calculate(int x, int y) {
        // return an int type value
        return x + y;
    }

    public void print() {
        System.out.println("void method");

        // it does not need to contain a return statement, but it
        // may do so
        return;
    }

    public String getString() {
        return "return String type value";

        // try to execute a statement after return a value will
        // cause a compile-time error.
        //
        // String error = "error";
    }
}

class Dog {
    private String breed;
    private String name;

    Dog(String breed, String name) {
        this.breed = breed;
        this.name = name;
    }

    public Dog getDog() {
        // return Dog type
        return this;
    }

    public String toString() {
        return "breed: " + breed.concat("name: " + name);
    }
}

How do I invoke superclass constructor?

This example shows you how to use the super keyword to call a superclass constructor. The Female class constructor calls its superclass constructor and initializes its own initialization parameters. The call to the superclass constructor must be done in the first line of the constructor in the subclass.

package org.kodejava.example.fundamental;

public class Human {
    private String gender;
    private int age;

    public Human(String gender) {
        this.gender = gender;
    }
}

To call a superclass constructor we call super(). In the case below we call the superclass constructor with one string variable as a parameter.

package org.kodejava.example.fundamental;

public class Female extends Human {
    private String hairStyle;

    public Female(String hairStyle, String gender) {
        super(gender);
        this.hairStyle = hairStyle;
    }
}

How do I use the final keyword in Java?

The final modifier is used to mark a class final so that it cannot inherited, to prevent a method being overridden, and to prevent changing the value of a variable. Arguments of a method if declared as final is also can not be modified within the method.

package org.kodejava.example.fundamental;

public class FinalExample {
    // breed is declared final.
    // can't change the value assigned to breed
    public final String breed = "pig";
    private int count = 0;

    // sound() method is declared final, so it can't be overridden
    public final void sound() {
        System.out.println("oink oink");
    }

    // number parameter is declared final. can't change the value
    // assigned to number
    public int count(final int number) {
        // assign a value to number variable will cause a
        // compile-time error
        //
        // number = 1;

        count = +number;
        return count;
    }

    public static void main(String[] args) {
        FinalExample fe = new FinalExample();
        // assign a value to breed variable will cause a
        // compile-time error
        //
        // fe.breed = "dog";

        int number = fe.count(20);
    }
}

final class SubFinalExample extends FinalExample {

    // try to override sound() method of superclass will cause a
    // compile-time error
    //
    // public void sound() {
    //     System.out.println("oink");
    // }
}

// try to inherit a class that declared final will cause a
// compile-time error
//
class OtherFinalExample extends SubFinalExample {
}