To Handle Ad Blocker

Java Generic

The Java Generics programming is introduced in J2SE 5 to deal with type-safe objects. Before generics, we can store any type of objects in collection i.e. non-generic. Now generics, forces the java programmer to store specific type of objects.

Advantage of Java Generics

There are mainly 3 advantages of generics. They are as follows:
  1. Type-safety: We can hold only a single type of objects in generics. It doesn’t allow to store other objects.

  2. Type casting is not required: There is no need to typecast the object.
    Before Generics, we need to type cast After Generics, we don't need to typecast the object
    List list = new ArrayList();
    list.add("hello");
    String s = (String) list.get(0);//typecasting     		List<String> list = new ArrayList<String>();
    list.add("hello");
    String s = list.get(0);


  3. Compile-Time Checking: It is checked at compile time so problem will not occur at runtime. The good programming strategy says it is far better to handle the problem at compile time than runtime.

    List list = new ArrayList();
    list.add("hello");
    list.add(32); //Compile Time Error

    Syntax to use generic collection - ClassOrInterface <type>
    Simple example to use Generics - ArrayList <string>

Full Example of Java Generics

Here, we are using the ArrayList class, but you can use any collection class such as ArrayList, LinkedList, HashSet, TreeSet, HashMap, Comparator etc. Now we are going to use map elements using generics. Here, we need to pass key and value. Let us understand it by a simple example:
import java.util.*;

class Simple
{
public static void main(String args[])
{
ArrayList<String> list=new ArrayList<String>();
list.add("rahul");
list.add("jai");
//list.add(32);//compile time error
String s=list.get(1);//type casting is not required
System.out.println("element is: "+s);
Iterator<String> itr=list.iterator();
while(itr.hasNext())
{
System.out.println(itr.next());
}
}
}		 import java.util.*;

class Test
{
public static void main(String args[])
{
Map<Integer,String> map=new HashMap<Integer,String>();
map.put(1,"vijay");
map.put(4,"umesh");
map.put(2,"ankit");

//Now use Map.Entry for Set and Iterator
Set<Map.Entry<Integer,String>> set=map.entrySet();
Iterator<Map.Entry<Integer,String>> itr=set.iterator();
while(itr.hasNext())
{
Map.Entry e=itr.next();//no need to typecast
System.out.println(e.getKey()+" "+e.getValue());
}
}
}
Output:element is:
jai
rahul
jai 		Output:
1 vijay
2 ankit
4 umesh


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