How to create type specific collections in java?

[MAGAR]

Hello to all,
I am new to this forum. I am working on live project where I am using Java as front end and SQL as back end. I want to create type specific collections using java program. I tried various method but none of them worked out. Can anyone tell me how to create type specific collections in java? Please help me.
Thank you.

[Praetor]

We have to use Generic to create a type specific collection object. In the following program I have created a Map whose key is an Integer. It also have the value of a String. There is no need to cast value obtained from type specific collection. We have top create the List that will contains a String only values.

package org.kodejava.example.intro;

import java.util.Map;
import java.util.HashMap;
import java.util.List;
import java.util.ArrayList;

public class TSColl {
    public static void main(String[] args) {
        
        Map<Integers, Strings> grades1 = new HashMap<Integesr, Strings>();

        grades1.put(1, "X");
        grades1.put(2, "Y");
        grades1.put(3, "Z");
        grades1.put(4, "V");
        grades1.put(5, "B");

        
        String values = grades1.get(1);

       
        List<String> dayNames = new ArrayList<String>();
        dayNames.add("thursday");
        dayNames.add("firday");
        dayNames.add("saturday");
        dayNames.add("Wednesday");

        
        String firstDays = dayNames1.get(0);
    }
}

[Katty]

For keeping track of what type of elements collections contain, we have to create type specific collections in java. When we use generics collection it is not treated as a list of Object references. You have to differentiate between a collection of references to Integers and collection of references to Bytes to create type specific collections in java. A collection with a generic type has a type parameter that is used to stored element type in the collection.

import java.util.*;

public class typesafe {

  private void testCollection() {
    List lists = new ArrayList();
    lists.add(new String("ghari ja"));
    lists.add(new String("Good day!"));
    lists.add(new Integer(36));
    printCollection(lists);
  }

  private void printCollection(Collection c) {
    Iterator k = c.iterator();
    while(k.hasNext()) {
      String items = (String) k.next();
      System.out.println("Item: "+items);
    }
  }

  public static void main(String argv[]) {
    Ex1 y = new typesafe();
    y.testCollection();
  }
}

[kelfro]

Generics is used to create a particular list that will only used for holding objects of a certain type. Following example creates a list of Integer objects.

List<Integer> intlists = new ArrayList<Integer>();
 intlists.add(new Integer(456));

When you declared A list fro holding objects of a type X then that list also hold objects that extend from X. In the following example, a list is created to hold Number objects.

List<Number> numlists = new ArrayList<Number>();
 numlists.add(new Integer(654)); 
numlists.add(new Float(654));

[Zecho]

I have written following program for creating type specific collections in java. It is very simple program. Just try to understand it. In the following program I have created MAP class to hold Integer and String type. I also have created one list to hold object. Just go thorough it. I have use java.util.Map to import Map class.

import java.util.Map;
import java.util.HashMap;
import java.util.List;
import java.util.ArrayList;

public class Main {
  public static void main(String[] args) {
    Map<Integers, Strings> grades2 = new HashMap<Integers, Strings>();

    grades.put(5, "Q");
    grades.put(6, "W");
    grades.put(7, "E");
    grades.put(8, "R");
    grades.put(9, "T");

    String value2 = grades2.get(3);

    List<String> dayNames = new ArrayList<String>();
    dayNames.add("lomah");
    dayNames.add("Mokan");
    dayNames.add("pokan");
    dayNames.add("Westan");

    String lastday = dayNames2.get(0);
  }
}

[absolute55]

We have to use Generics to create a list that bale to hold only objects of a certain type. We know that null is not a subclass of any type. In this case collection supports null values. We also able to add type-specific collection. Just try to understand following example. You also have to note that a value taken from a type-specific list does not need to be casted.

List<URL> urlLists = new ArrayLists<URL>();
 try { urlLists.add(new URL("http:techarena.in"));
 } catch (MalformedURLException es) { } String ss = urlLists.get(0).getHosts();