Collections Map

Map:

• Map is key-value pair.
• Map Interface represents a mapping between key and value.
• Map having:

1. HashMap
2. LinkedHashMap
3. HashaTable
4. TreeMap

HashMap:

• HashMap is not synchronized.
• Hashmap allows one key null and multiple null values.
• HashMap default capacity is :

static final int DEFAULT_INITIAL_CAPACITY =16 static final float DEFAULT_LOAD_FACTOR = 0.75f;

Program for HashMap:

package com.instanceofjava;

import java.util.HashMap;

import java.util.Iterator;

import java.util.Map;

import java.util.Map.Entry;

public class Hashmap2 {

/**

* @param args

*/

public static void main(String[] args) {

// TODO Auto-generated method stub

HashMap map=new HashMap();

map.put(1, "indhu");

map.put("d", "sindhu");

map.put("3", "swathi");

map.put(null, "indhira");
map.put(null, "indhira");
map.put(4, "sindhu");

if(!map.isEmpty()){

Iterator it=map.entrySet().iterator();

while(it.hasNext()){

Map.Entry obj=(Entry) it.next();

System.out.println(obj.getValue());

}

}

}

Output:

indhira
swathi
indhu
sindhu
sindhu

HashTable:

• HashTable is synchronized.
• HashTable doesn't allow any null key or any null values.
• HasTable Default capacity:

static final int DEFAULT_INITIAL_CAPACITY = 11;static final float DEFAULT_LOAD_FACTOR = 0.75f;
Program for HashTable:

package com.instanceofjava;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;

public class Hashtable3{

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Hashtable hashTable=new Hashtable();
hashTable.put(1, "indhu");
hashTable.put("d", "sindhu");
hashTable.put("3", "swathi");
hashTable.put("d", "sindhu");
if(!hashTable.isEmpty()){
Iterator it=hashTable.entrySet().iterator();
while(it.hasNext()){
Map.Entry obj=(Entry) it.next();
System.out.println(obj.getValue());
}


}
}

}

Output:

swathi

sindhu

indhu

TreeMap:

• TreeMap is sorted order.
• TreeMap doesn't allow null key or null values.

Program for TreeMap:

package com.instanceofjava;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.TreeMap;

public class Employee{

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
TreeMap treeMap=new TreeMap();
treeMap.put("g", "indhu");
treeMap.put("d", "sindhu");
treeMap.put("3", "swathi");
treeMap.put("d", "sindhu");
if(!treeMap.isEmpty()){
Iterator it=treeMap.entrySet().iterator();
while(it.hasNext()){
Map.Entry obj=(Entry) it.next();
System.out.println(obj.getValue());
}


}
}

}

Output:

swathi

sindhu

indhu