Object Methods - AP Computer Science A

Creating Methods

We've already talked about methods and how to create them.

Here's a quick example of a method that does some calculation, and prints the result:

Java

public static void doMath(int x) {
x += 17;
x *= 4;
x %= 2;
System.out.println(x);
}

Getter Methods

Getter methods allow us to get the object attributes of each object. These are non-void, as they return a value.

Here's an example of a Getter Method:

Java

public String getColor() {
return color;
}

And in our main method, we can use it like this:

Java

System.out.println(tesla.getColor()); // prints Red
System.out.println(motorcycle.getColor()); // prints Blue
System.out.println(malibu.getColor()); // prints Silver

You will want to create a Getter method for every variable you want to access after creating the object.

Setter Methods

Setter methods allow us to set the object attributes of each object. These are void, as they do not return a value.

Here's an example of a Setter Method:

Java

public String setColor(String color) {
this.color = color;
}

And in our main method, we can use it like this:

Java

tesla.setColor("White");
motorcycle.setColor("Black");
malibu.setColor("Gray");

System.out.println(tesla.getColor()); // prints White
System.out.println(motorcycle.getColor()); // prints Black
System.out.println(malibu.getColor()); // prints Gray

You will want to create a Setter method for every variable you want to change after creating the object.

toString()

And, of course, the toString() method. This is built into every object, just by putting it in a print or println.

We write a toString() like so:

Java

public String toString() {
  String message;
  if(isElectric) {
    message = "is electric";
  } else {
    message = "is not electric";
  }

  return "This vehicle is a " + color + " " + model + " " + type + " that " + message + " and costs $"+cost+".";
}

And call it in the main method like this:

Java

System.out.println(tesla);
System.out.println(motorcycle);
System.out.println(malibu);

This prints:

Text

This vehicle is a Red Tesla Model 3 Sedan that is electric and costs $35000.
This vehicle is a Blue Harley-Davidson LiveWire Motorcycle that is electric and costs $30000.
This vehicle is a Silver Chevy Malibu Sedan that is not electric and costs $23000.

Try playing with Getter/Setter and toString() methods, and see what you can do!