Java Generics Methods Examples

In Java Generics, like Generic Classes and Interfaces we can have Generic Methods with their own type parameters.

Example 1: Compare two values

public class Example1 {

    public <T> boolean areEqual(T value1, T value2) {
        return value1.equals(value2);
    }

    public static void main(String[] args) {

        Example1 example = new Example1();

        int num1 = 10;
        int num2 = 10;
        boolean isEqual1 = example.areEqual(num1, num2);
        System.out.println(num1 + " = " + num2 + " ? " + isEqual1);

        String str1 = "Sam";
        String str2 = "Sammy";
        boolean isEqual2 = example.areEqual(str1, str2);
        System.out.println(str1 + " = " + str2 + " ? " + isEqual2);

        String val1 = "1";
        int val2 = 1;
        boolean isEqual3 = example.areEqual(val1, val2);
        System.out.println(val1 + " = " + val2 + " ? " + isEqual3);

    }
}

Output:

Example 2: Find First Occurrence of an Element in an Array

import java.util.List;

public class Example2 {
    
    public <T> int findIndex(T[] array, T target) {
        for (int i = 0; i < array.length; i++) {
            if (array[i].equals(target)) {
                return i;
            }
        }
        return -1; //Not Found!
    }

    public <T> int countOccurrences(List<T> list, T target) {
        int count = 0;
        for (T item : list) {
            if (item.equals(target)) {
                count++;
            }
        }
        return count;
    }

    public static void main(String[] args) {
        Example2 example = new Example2();

        Integer[] intArray1 = { 1, 2, 3, 4, 5 };
        int index1 = example.findIndex(intArray1, 3);
        System.out.println("Index of 3 in the array is: " + index1);

        String[] strArray = { "China", "Japan", "India", "USA", "Canada" };
        int index2 = example.findIndex(strArray, "USA");
        System.out.println("Index of 'USA' in the array is: " + index2);

        Integer[] intArray2 = { 5, 6, 2, 4, 6, 7, 8, 1, 9 };
        int index3 = example.findIndex(intArray2, 17);
        System.out.println("Index of 17 in the array is: " + index3);

    }
}

Output:

Example 3: Count Occurrences of an Element in a List

import java.util.Arrays;
import java.util.List;

public class Example3 {

    public <T> int countOccurrences(List<T> list, T target) {
        int count = 0;
        for (T item : list) {
            if (item.equals(target)) {
                count++;
            }
        }
        return count;
    }

    public static void main(String[] args) {
        Example3 example = new Example3();

        List<String> names = Arrays.asList("Japan", "China", "Japan", "Australia", "India", "Japan");
        int count1 = example.countOccurrences(names, "Japan");
        System.out.println("Occurrences of 'Japan' in the list: " + count1);

        List<Integer> numbers = Arrays.asList(3, 4, 6, 9, 3);
        int count2 = example.countOccurrences(numbers, 3);
        System.out.println("Occurrences of '3' in the list: " + count2);
    }
}

Output: