Java Tutorial - 8 Generic

Introduction

Generic type is a special type in Java that allows specific data type as a parameter. The generic type is useful to specify the data type in a class instead of making separated classes for each type. This is the comparison between class creation without using generic type and class creation with generic type.

// without generic type, the class for each type is created
class IntBox {
    private int content;
}

class StringBox {
    private String content;
}

// with generic type with <T> syntax
class Box<T> {
    private T content;
}

Creating Generic Type

This is the basic syntax of using generic type

class_name<T1,T2,....,n>

The generic type is declared by using <T> syntax (the T character can be changed with other character, usually the T character is used to define generic). In this example, the generic type is implemented in a class called Box.

// create a class called Box with generic type called "T"
public class Box<T> {
    // using "T" as generic type
    private T content;

    // constructor
    public Box(T content) {
        this.content = content;
    }

    public T getContent() {
        return content;
    }

    public void setContent(T content) {
        this.content = content;
    }
}

Main Class

public class MyApp {
    public static void main(String[] args) {
        // using String as a data type
        Box<String> stringBox = new Box<>("Generic is Cool!");

        // using Integer as a data type
        Box<Integer> intBox = new Box<>(12);

        // print out the content
        System.out.println(stringBox.getContent());
        System.out.println(intBox.getContent());
    }
}

Output

Generic is Cool!
12

Based on the code above, the data type is specified inside the angle bracket (<>). The data type that can be used is a reference data type.

In this example, the multiple generic type is used in class called Pair.

public class Pair<K,V> {
    private K key;
    private V value;

    public Pair(K key, V value) {
        this.key = key;
        this.value = value;
    }

    public K getKey() {
        return key;
    }

    public void setKey(K key) {
        this.key = key;
    }

    public V getValue() {
        return value;
    }

    public void setValue(V value) {
        this.value = value;
    }
}

Based on the code above, the multiple generic type (<K,V>) is used.

Main Class

public class MyApp {
    public static void main(String[] args) {
        Pair<Integer, String> myPair = new Pair<>(1,"Test");

        // get the key and value
        System.out.println(myPair.getKey());
        System.out.println(myPair.getValue());
    }
}

Output

1
Test

Based on the code above, the required types is define inside angle bracket separated by comma (,).

Sources

• Learn more about generic type in this link.

I hope this article is helpful for learning the Java programming language. If you have any thoughts or comments you can write in the discussion section below.