package com.kartik.tutorials;public class MyEntry<K, V> { private final K
key; private V value; public MyEntry(K
key, V value) { this.key = key; this.value =
value; } public K getKey()
{ return key; } public V
getValue() { return value; } public void
setValue(V value) { this.value =
value; }}
This is the map implementation based on MyEntry.
package com.kartik.tutorials;import java.util.Arrays;import java.util.HashSet;import java.util.Set;public class MyMap<K, V> { private int size; private int
DEFAULT_CAPACITY = 16; @SuppressWarnings("unchecked") private
MyEntry<K, V>[] values = new MyEntry[DEFAULT_CAPACITY]; public V get(K
key) { for (int i = 0;
i < size; i++) { if (values[i]
!= null) { if
(values[i].getKey().equals(key)) { return
values[i].getValue(); } } } return null; } public void put(K
key, V value) { boolean insert
= true; for (int i = 0;
i < size; i++) { if
(values[i].getKey().equals(key)) {
values[i].setValue(value); insert =
false; } } if (insert) { ensureCapa();
values[size++] = new MyEntry<K, V>(key, value); } } private void
ensureCapa() { if (size ==
values.length) { int newSize =
values.length * 2; values =
Arrays.copyOf(values, newSize); } } public int size()
{ return size; } public void
remove(K key) { for (int i = 0;
i < size; i++) { if
(values[i].getKey().equals(key)) { values[i] =
null; size--;
condenseArray(i); } } } private void
condenseArray(int start) { for (int i =
start; i < size; i++) { values[i] =
values[i + 1]; } } public
Set<K> keySet() { Set<K>
set = new HashSet<K>(); for (int i = 0;
i < size; i++) {
set.add(values[i].getKey()); } return set; }}
And a small test.
package com.kartik.tutorials;import static org.junit.Assert.assertEquals;import java.util.HashMap;import java.util.Map;import org.junit.Before;import org.junit.Test;public class MyMapTest { @Before public void
setUp() throws Exception { } @Test public void
testStandardMap() { // Standard
Map Map<String,
Integer> map = new HashMap<String, Integer>(); map.put("Lars",
1); map.put("Lars",
2); map.put("Lars",
1);
assertEquals(map.get("Lars"), 1); for (int i = 0;
i < 100; i++) {
map.put(String.valueOf(i), i); }
assertEquals(map.size(), 101);
assertEquals(map.get("51"), 51); map.keySet(); } @Test public void
testMapMap() { // MyMap
MyMap<String, Integer> map = new MyMap<String, Integer>(); map.put("Lars",
1); map.put("Lars",
2); map.put("Lars",
1);
assertEquals(map.get("Lars"), 1); for (int i = 0;
i < 100; i++) {
map.put(String.valueOf(i), i); }
assertEquals(map.size(), 101);
assertEquals(map.get("51"), 51); }} 
I am Kartik Chandra Mandal from Bangalore, India. Working as software engineer in Java technology. Have good knowledge of OWASP and CSRF in security for applications and it's implementation in Java technology.