GenDemo67.java

/*
We use generic concept to provide type safety and to resolve
type casting problem
in this example using one class defined in collection framework(API)
with and without generics
 */

import java.util.ArrayList;

public class GenDemo67 {
  public static void main(String[] args) {
    // arrays are by-default type safe and there is no need of type casting
    // The problem with array is that its size is fixed.
    // we use collection framework classes to hold homogeneous and
    // heterogeneous data elements and also its size is not fixed
    // and we use generics with  classes defined in collection framework to
    // provide type safety and to resolve type casting problem
    // Example:-

    Integer arr[]= new Integer[10];
    arr[0]= 50;
    arr[1]= 60;
    arr[2] = "neeraj"; // it will generate compile time error incompatible type

    // Second Senerio
    // using ArrayList class of collection API without generics
    // Collection objects are not type safe if our requirement is to add only
    // Integer objects to the ArrayList, By mistake if we are trying to insert
    // any other element we will not  get any comple time error
    // as shown in the following lines
    ArrayList i = new ArrayList();
    i.add(10);     // remember it is autoboxing here 
    i.add(15);
    i.add(20);
    i.add("Neeraj");

    // if we  retrieve values from ArrayList and assign to another variable
    // type casting is required
    Integer val3 = i.get(2); // observe the error
    Integer val1 = (Integer) i.get(2);  // type casting required
    String val2 = String.valueOf(i.get(1));
    System.out.println(val1 + "   "+ val2);

    // Generic version of ArrayList
    
    ArrayList<String> s1 = new ArrayList<>();
    s1.add("neeraj");
    s1.add("kamal");
    // you can only hold String values  generic provide type safety
    s1.add(new Integer(67)); 
    s1.add(68);
    
    // generic resolve type casting problem 
    String a90 = s1.get(1);
    
    // to print all values stored in ArrayList we use forEach loop
    for (String res:s1) 
    {
      System.out.println(res); 
    }

  }
}