JAVA EE: Java Tutorial: Generics in java [Generic Interface and Class using multiple type parameters]

Monday 15 May 2017

Java Tutorial: Generics in java [Generic Interface and Class using multiple type parameters]

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OrderedPair.java

/**
 * Multiple Type Parameters
 */
interface Pair<K, V>
{
    public K getKey();

    public V getValue();
}

/**
 * As mentioned previously, a generic class can have multiple type parameters.
 * For example, the generic OrderedPair class, which implements the generic Pair
 * interface
 */
public class OrderedPair<K, V> implements Pair<K, V>
{

    private K key;
    private V value;

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

    public K getKey()
    {
        return key;
    }

    public V getValue()
    {
        return value;
    }
}

GenericDemo.java

import java.util.ArrayList;
import java.util.List;

public class GenericDemo
{

    public static void main(String[] args)
    {
        Pair<String, Integer> pair1 = new OrderedPair<String, Integer>("age", 12);
        System.out.println(pair1.getKey() + "=" + pair1.getValue());

        Pair<String, String> pair2 = new OrderedPair<String, String>("user", "root");
        System.out.println(pair2.getKey() + "=" + pair2.getValue());

        List<String> nameList = new ArrayList<>();
        nameList.add("Peter");
        nameList.add("Ram");

        /*
         * We can also substitute a type parameter (i.e., K or V) with
         * a parameterized type (i.e., List<String>).
         */
        Pair<String, List<String>> pair3 = new OrderedPair<String, List<String>>(
                                                                   "names", nameList);
        System.out.println(pair3.getKey() + "=" + pair3.getValue());

    }

}