Methods

Methods (also called functions) are the things an object can do. There are two kinds of methods:

Methods that return a value
Methods that don't return a value

Here are two examples of each:

This method returns (reports back) the person's height in inches

public double heightToInches() {
    // 1 meter = 39.97 inches
    double answer = myHeight * 39.97;
    return answer;
}

This method returns (reports back) the person's name

public String getName() {
    return myName;
}

This method prints info about the Person, but doesn't return any values

public void printInfo() {
    String response;
    response = "Hello, my name is " + myName;
    response = response + " and I'm " + myAge + " years old!";
    if (isStudent == true) {
        response += " I am a student.";
    }
    else {
        response += " I am not a student.";
    }
    System.out.println(response);
}

This method increases the Person's age by a given amount, but doesn't return any values

public void increaseAge(int amount) {
    myAge = myAge + amount;
}

Adding these methods to our Person class, we have:

public class Person {

    // Instance Variables - fields storing info about the state
    //                      of an object (attributes/properties)

    int myAge;          // Age in years
    double myHeight;    // Height in meters
    boolean isStudent;  // True if enrolled at any school, false otherwise
    String myName;      // Person's name


    // Constructors - Specialized methods that set an object up
    //                and initialize instance variables

    public Person() {        
        myAge = 17;
        myHeight = 1.53;
        isStudent = false;
        myName = "Frances";
    }

    public Person(int age, double height, boolean student, String name) {
        myAge = age;
        myHeight = height;
        isStudent = student;
        myName = name;
    }

    // Methods - The things an object can do
    //           Subroutines, or code, that define how an object behaves
    public double heightToInches() {
        // 1 meter = 39.97 inches
        double answer = myHeight * 39.97;
        return answer;
    }

    public String getName() {
        return myName;
    }

    public void printInfo() {
        String response;
        response = "Hello, my name is " + myName;
        response = response + " and I'm " + myAge + " years old!";
        if (isStudent == true) {
            response += " I am a student.";
        }
        else {
            response += " I am not a student.";
        }
        System.out.println(response);
    }

    public void increaseAge(int amount) {
        myAge = myAge + amount;
    }
}

A few things to notice:

Methods that return values specify the data type they return:

public data_type method_name () {  
...  
)

Methods that don't return values have void as the return type

public void method_name () {  
    ...  
)

Methods can have parameters that will affect the method results. In this case, age will be increased by the amount passed in to the parameter.

public void increaseAge (int amount) {  
...  
)

You may have noticed all the methods and constructors we declared started with the public access modifier. We will discuss access modifiers later.

Constructors

Getters And Setters

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Outline

Methods

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