Java Class Methods

Java Class Methods

You learned from the Java Methods chapter that methods are declared within a class, and that they are used to perform certain actions:

public class Main {
  static void myMethod() {
    System.out.println("Hello World!");
  }
}

myMethod() prints a text (the action), when it is called. To call a method, write the method's name followed by two parentheses () and a semicolon;

Example

public class Main {
  static void myMethod() {
    System.out.println("Hello World!");
  }

  public static void main(String[] args) {
    myMethod();
  }
}

// Outputs "Hello World!"

Access Methods With an Object

Example

// Create a Main class
public class Main {

  // Create a fullThrottle() method
  public void fullThrottle() {
    System.out.println("The car is going as fast as it can!");
  }

  // Create a speed() method and add a parameter
  public void speed(int maxSpeed) {
    System.out.println("Max speed is: " + maxSpeed);
  }

  // Inside main, call the methods on the myCar object
  public static void main(String[] args) {
    Main myCar = new Main();   // Create a myCar object
    myCar.fullThrottle();      // Call the fullThrottle() method
    myCar.speed(200);          // Call the speed() method
  }
}

// The car is going as fast as it can!
// Max speed is: 200

Example explained

1. We created a custom Main class with the class keyword.

2. We created the fullThrottle() and speed() methods in the Main class.

3. The fullThrottle() method and the speed() method will print out some text, when they are called.

4. The speed() method accepts an int parameter called maxSpeed - we will use this in 8).

5. In order to use the Main class and its methods, we need to create an object of the Main Class.

6. Then, go to the main() method, which you know by now is a built-in Java method that runs your program (any code inside main is executed).

7. By using the new keyword we created an object with the name myCar.

8. Then, we call the fullThrottle() and speed() methods on the myCar object, and run the program using the name of the object (myCar), followed by a dot (.), followed by the name of the method (fullThrottle(); and speed(200);). Notice that we add an int parameter of 200 inside the speed() method.

Note: Remember that.. The dot (.) is used to access the object's attributes and methods. To call a method in Java, write the method name followed by a set of parentheses (), followed by a semicolon (;). A class must have a matching filename (Main and Main.java).

Using Multiple Classes

Like we specified in the Classes chapter, it is a good practice to create an object of a class and access it in another class.

Remember that the name of the java file should match the class name. In this example, we have created two files in the same directory:

• Main.java
• Second.java

public class Main {
  public void fullThrottle() {
    System.out.println("The car is going as fast as it can!");
  }

  public void speed(int maxSpeed) {
    System.out.println("Max speed is: " + maxSpeed);
  }
}

When both files have been compiled:

C:\Users\Your Name>javac Main.java
C:\Users\Your Name>javac Second.java

Run the Second.java file:

C:\Users\Your Name>java Second

And the output will be:

<code>The car is going as fast as it can!<br/>
Max speed is: 200
</code>