Java Generic Interface Examples

The Generalized Syntax for a Generic Interface

interface interfaceName<type-param-list> { // ...
}

class className<type-param-list>
           implements interfaceName<type-param-list> {
     // ....
}

• type-param-list is a comma-separated list of type parameters.
• when a generic interface is implemented, you must specify the type arguments

Java Generic Interface Examples

Let's write an simple example to find minimum and maximum value of Integer, character and String array.

1. Create three arrays - Integer, character and String array.
2. Write generic methods to find minimun and maximun value of an any type of array.

/**
 * Generic interface example to find min and max of array.
 * @author javaguides.net
 *
 */
public class GenericInterfaceExample {
	public static void main(String args[]) {
		Integer intOfArray[] = { 3, 6, 2, 8, 6 };
		Character charOfArray[] = { 'A', 'r', 'V', 'w' };
		String strOfArray[] = {"abc", "xyz", "pqr"};
		
		MinMaxImpl<Integer> intMinMax = new MinMaxImpl<Integer>(intOfArray);
		MinMaxImpl<Character> charMinMax = new MinMaxImpl<Character>(charOfArray);
		MinMaxImpl<String> strMinMax = new MinMaxImpl<String>(strOfArray);

		System.out.println("Max value in intOfArray: " + intMinMax.max());
		System.out.println("Min value in intOfArray: " + intMinMax.min());

		System.out.println("Max value in charOfArray: " + charMinMax.max());
		System.out.println("Min value in charOfArray: " + charMinMax.min());
		
		System.out.println("Max value in strOfArray: " + strMinMax.max());
		System.out.println("Min value in strOfArray: " + strMinMax.min());
	}
}

interface MinMax<T extends Comparable<T>> {
	T min();

	T max();
}

class MinMaxImpl<T extends Comparable<T>> implements MinMax<T> {
	T[] vals;

	MinMaxImpl(T[] o) {
		vals = o;
	}

	public T min() {
		T v = vals[0];

		for (int i = 1; i < vals.length; i++) {
			if (vals[i].compareTo(v) < 0) {
				v = vals[i];
			}
		}

		return v;
	}

	public T max() {
		T v = vals[0];

		for (int i = 1; i < vals.length; i++) {
			if (vals[i].compareTo(v) > 0) {
				v = vals[i];
			}
		}

		return v;
	}
}

Output:

Max value in intOfArray: 8
Min value in intOfArray: 2
Max value in charOfArray: w
Min value in charOfArray: A
Max value in strOfArray: xyz
Min value in strOfArray: abc