JAVA

generic classes in java

// A Simple Java program to show multiple
// type parameters in Java Generics
  
// We use < > to specify Parameter type
class Test<T, U>
{
    T obj1;  // An object of type T
    U obj2;  // An object of type U
  
    // constructor
    Test(T obj1, U obj2)
    {
        this.obj1 = obj1;
        this.obj2 = obj2;
    }
  
    // To print objects of T and U
    public void print()
    {
        System.out.println(obj1);
        System.out.println(obj2);
    }
}
  
// Driver class to test above
class Main
{
    public static void main (String[] args)
    {
        Test <String, Integer> obj =
            new Test<String, Integer>("GfG", 15);
  
        obj.print();
    }
}

java define a generic class that produces

List<String> list1 = new ArrayList<String>(); // java 7 ? List<String> list1 = new ArrayList<>(); 
list1.add("abc");
//list1.add(new Integer(5)); //compiler error

for(String str : list1){
     //no type casting needed, avoids ClassCastException
}

java define a generic class that produces

List list = new ArrayList();
list.add("abc");
list.add(new Integer(5)); //OK

for(Object obj : list){
	//type casting leading to ClassCastException at runtime
    String str=(String) obj; 
}