Java Tutorial - How to create Generic Method in Java

It is possible to create a generic method that is enclosed within a non-generic class.

public class Main {
 static <T, V extends T> boolean isIn(T x, V[] y) {
 for (int i = 0; i < y.length; i++) {
 if (x.equals(y[i])) {
 return true;
 }//www.java2s.com
 }
 return false;
 }
 public static void main(String args[]) {
 Integer nums[] = { 1, 2, 3, 4, 5 };
 if (isIn(2, nums)){
 System.out.println("2 is in nums");
 }
 String strs[] = { "one", "two", "three", "four", "five" };
 if (isIn("two", strs)){
 System.out.println("two is in strs");
 }
 }
}

The code above generates the following result.

Example

The following code declares a copyList() generic method.

/*www.java2s.com*/
import java.util.ArrayList;
import java.util.List;
public class Main {
 public static void main(String[] args) {
 List<String> ls = new ArrayList<String>();
 ls.add("A");
 ls.add("B");
 ls.add("C");
 List<String> lsCopy = new ArrayList<String>();
 copyList(ls, lsCopy);
 List<Integer> lc = new ArrayList<Integer>();
 lc.add(0);
 lc.add(5);
 List<Integer> lcCopy = new ArrayList<Integer>();
 copyList(lc, lcCopy);
 }
 static <T> void copyList(List<T> src, List<T> dest) {
 for (int i = 0; i < src.size(); i++)
 dest.add(src.get(i));
 }
}

Java Generic Constructors

It is possible for constructors to be generic, even if their class is not. For example, consider the following short program:

class MyClass {/*fromwww.java2s.com*/
 private double val;
 <T extends Number> MyClass(T arg) {
 val = arg.doubleValue();
 }
 void showval() {
 System.out.println("val: " + val);
 }
}
public class Main {
 public static void main(String args[]) {
 MyClass test = new MyClass(100);
 MyClass test2 = new MyClass(123.5F);
 test.showval();
 test2.showval();
 }
}

The code above generates the following result.