Hellostatic_ipynb_2_ • 9 min read

// Define Class with Constructor returning Object
public class HelloObject {
    private String hello;   // instance attribute or variable
    public HelloObject() {  // constructor
        hello = "Hello, World!";
    }
    public String getHello() {  // getter, returns value from inside the object
        return this.hello;  // return String from object
    }
    public static void main(String[] args) {    
        HelloObject ho = new HelloObject(); // Instance of Class (ho) is an Object via "new HelloObject()"
        System.out.println(ho.getHello()); // Object allows reference to public methods and data
    }
}
// IJava activation
HelloObject.main(null);

Hello, World!

// Define Class
public class HelloDynamic { // name the first letter of class as capitalized, note camel case
    // instance variable have access modifier (private is most common), data type, and name
    private String hello;
    // constructor signature 1, public and zero arguments, constructors do not have return type
    public HelloDynamic() {  // 0 argument constructor
        this.setHello("Chill!");  // using setter with static string
    }
    // constructor signature, public and one argument
    public HelloDynamic(String hello) { // 1 argument constructor
        this.setHello(hello);   // using setter with local variable passed into constructor
    }
    // setter/mutator, setter have void return type and a parameter
    public void setHello(String hello) { // setter
        this.hello = hello;     // instance variable on the left, local variable on the right
    }
    // getter/accessor, getter used to return private instance variable (encapsulated), return type is String
    public String getHello() {  // getter
        return this.hello;
    }
    // public static void main(String[] args) is signature for main/drivers/tester method
    // a driver/tester method is singular or called a class method, it is never part of an object
    public static void main(String[] args) {  
        HelloDynamic hd1 = new HelloDynamic(); // no argument constructor
        HelloDynamic hd2 = new HelloDynamic("Hello, Nighthawk Coding Society!"); // one argument constructor
        System.out.println(hd1.getHello()); // accessing getter
        System.out.println(hd2.getHello()); 
    }
}
// IJava activation
HelloDynamic.main(null);

Chill!
Hello, Nighthawk Coding Society!

public class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.setName(name);
        this.setAge(age);
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setAge(int age) {
        if(age >= 0) {
            this.age = age;
        }
    }

    public String getName() {
        return this.name;
    }

    public int getAge() {
        return this.age;
    }

    public static void main(String[] args) {  
        Person p1 = new Person("Vishnu", 17);
        System.out.println(p1.getName());
        System.out.println(p1.getAge());
    }
}

Person.main(null);

Vishnu
17

public class Dessert {
    private String type;
    private double cost;

    public Dessert(String type, double cost) {
        this.setType(type);
        this.setCost(cost);
    }

    public void setType(String type) {
        this.type = type;
    }

    public void setCost(double cost) {
        this.cost = cost;
    }

    public String getType() {
        return type;
    }

    public double getCost() {
        return cost;
    }

    public static void main(String[] args) {  
        Dessert dessert1 = new Dessert("cake", 8.99);
        System.out.println(dessert1.getType());
        System.out.println(dessert1.getCost());
    }
}

Dessert.main(null);

cake
8.99

public class Location {
    private String city;
    private String state;
    private String zip;

    public Location(String city, String state, String zip) {
        this.setCity(city);
        this.setState(state);
        this.setZip(zip);
    }

    public void setCity(String city) {
        this.city = city;
    }

    public void setState(String state) {
        this.state = state;
    }

    public void setZip(String zip) {
        this.zip = zip;
    }

    public String getCity() {
        return city;
    }

    public String getState() {
        return state;
    }

    public String getZip() {
        return zip;
    }

    @Override
    public String toString() {
        return "City: " + city + ", State: " + state + ", Zip: " + zip;
    }

    public static void main(String[] args) {
        Location loc = new Location("San Diego", "CA", "92127");
        System.out.println(loc);
    }
}

Location.main(null);

City: San Diego, State: CA, Zip: 92127