Java program for Map

By: Saravanan Emailed: 1766 times Printed: 2515 times    

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In this Tutorial we are going to see how to implement Map with arraylist. This is an example of a Map. We must import some of the packages as below.

import java.util.AbstractMap;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

public class MapExample extends AbstractMap

private List listk = new ArrayList();
private List listv = new ArrayList();

public Object put(Object key, Object value) 
Object result = get(key);
if (!listk.contains(key))
listv.set(listk.indexOf(key), value);
return result;

public Object get(Object key)
if (!listk.contains(key))
return null;
return listv.get(listk.indexOf(key));

public Set entrySet()
Set entries = new HashSet();
Iterator ki = listk.iterator();
Iterator vi = listv.iterator();
while (ki.hasNext())
entries.add(new Map11(,;
return entries;

public String toString()
StringBuffer s = new StringBuffer("{");
Iterator ki = listk.iterator(), vi = listv.iterator();
while (ki.hasNext())
s.append( + "=" +;
if (ki.hasNext())
s.append(", ");
return s.toString();

public static void main(String[] args)
MapExample m = new MapExample();
m.put("Netscape", "Mountain View, CA");
m.put("Adobe", "Mountain View, CA");
m.put("Sun", "Mountain View, CA");
m.put("Microsoft", "Redmond, WA");
m.put("IBM", "White Plains, NY");
m.put("O'Reilly", "Sebastopol, CA");
m.put("Learning Tree", "Los Angeles, CA");


class Map11 implements Entry, Comparable
Object key, value;
Map11(Object k, Object v)
key = k;
value = v;
public Object getKey()
return key;
public Object getValue()
return value;
public Object setValue(Object v)
Object result = value;
value = v;
return result;
public boolean equals(Object o) {
return key.equals(((Map11)o).key);
public int compareTo(Object rv) {
return ((Comparable)key).compareTo(

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