IdentityHashMapDemonstrator class
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Seshu Thanneeru
parent
09e0fa4e74
commit
f802d3d337
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package com.baeldung.map.identity;
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import java.util.*;
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public class IdentityHashMapDemonstrator {
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public static void main(String[] args) {
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IdentityHashMap<String, String> identityHashMap = createWithSimpleData();
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System.out.println("Map details: " + identityHashMap);
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IdentityHashMap<String, String> copiedMap = createFromAnotherMap(identityHashMap);
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updateWithNewValue(copiedMap);
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iterateIdentityHashMap(copiedMap);
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addNullKeyValue();
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demoHashMapVsIdentityMap(identityHashMap);
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demoMutableKeys();
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Map<String, String> synchronizedMap = getSynchronizedMap();
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//Do multithreaded operations on synchronizedMap
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}
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private static void addNullKeyValue() {
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IdentityHashMap<String, String> identityHashMap = new IdentityHashMap<>();
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identityHashMap.put(null, "Null Key Accepted");
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identityHashMap.put("Null Value Accepted", null);
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System.out.println(identityHashMap);
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}
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private static void iterateIdentityHashMap(IdentityHashMap<String, String> identityHashMap) {
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// Iterating using entrySet
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System.out.println("Iterating values: ");
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Set<Map.Entry<String, String>> entries = identityHashMap.entrySet();
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for (Map.Entry<String, String> entry: entries) {
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System.out.println(entry.getKey() + ": " + entry.getValue());
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}
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// Iterating using keySet
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System.out.println("Iterating values using keySet: ");
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for (String key: identityHashMap.keySet()) {
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System.out.println(key + ": " + identityHashMap.get(key));
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}
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// Throws error if we modify while iterating
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System.out.println("This iteration throws error: ");
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try {
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for (Map.Entry<String, String> entry: entries) {
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System.out.println(entry.getKey() + ": " + entry.getValue());
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identityHashMap.remove("title");
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}
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} catch (ConcurrentModificationException ex) {
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System.out.println("This exception will raise for sure, if we modify while iterating");
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}
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}
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private static class Book {
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String title;
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int year;
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Book() {
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// nothing to do
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}
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Book(String title, int year) {
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this.title = title;
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this.year = year;
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}
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@Override
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public boolean equals(Object o) {
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if (this == o) return true;
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if (o == null || getClass() != o.getClass()) return false;
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Book book = (Book) o;
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return year == book.year && title.equals(book.title);
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}
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@Override
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public int hashCode() {
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return Objects.hash(title, year);
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}
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@Override
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public String toString() {
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return "Book{" +
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"title='" + title + '\'' +
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", year=" + year +
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'}';
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}
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}
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private static void demoMutableKeys() {
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Book book1 = new Book("A Passage to India", 1924);
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Book book2 = new Book("Invisible Man", 1953);
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HashMap<Book, String> hashMap = new HashMap<>(10);
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IdentityHashMap<Book, String> identityHashMap = new IdentityHashMap<>(10);
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hashMap.put(book1, "A great work of fiction");
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identityHashMap.put(book1, "A great work of fiction");
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hashMap.put(book2, "won the US National Book Award");
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identityHashMap.put(book2, "won the US National Book Award");
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book2.year = 1952;
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System.out.println("Book2 from HashMap: " + hashMap.get(book2));
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System.out.println("Book2 from IdentityHashMap: " + identityHashMap.get(book2));
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System.out.println("HashMap: " + hashMap);
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System.out.println("IdentityHashMap: " + identityHashMap);
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}
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private static void demoHashMapVsIdentityMap(IdentityHashMap<String, String> identityHashMap) {
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HashMap<String, String> hashMap = new HashMap<>(identityHashMap);
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hashMap.put(new String("genre"), "Drama");
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identityHashMap.put(new String("genre"), "Drama");
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System.out.println("HashMap size: " + hashMap.size());
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System.out.println("IdentityHashMap size: " + identityHashMap.size());
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System.out.println("HashMap content: " + hashMap);
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System.out.println("IdentityHashMap content: " + identityHashMap);
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}
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private static Map<String, String> getSynchronizedMap() {
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Map<String, String> synchronizedMap = Collections.synchronizedMap(new IdentityHashMap<String, String>());
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return synchronizedMap;
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}
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private static IdentityHashMap<String, String> createFromAnotherMap(Map<String, String> otherMap) {
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IdentityHashMap<String, String> identityHashMap = new IdentityHashMap<>(otherMap);
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return identityHashMap;
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}
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private static void updateWithNewValue(IdentityHashMap<String, String> identityHashMap) {
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String oldTitle = identityHashMap.put("title", "Harry Potter and the Deathly Hallows");
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System.out.println("Old Title: " + oldTitle);
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System.out.println("Updated Title: " + identityHashMap.get("title"));
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}
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public static void addValue(IdentityHashMap<String, String> identityHashMap, String key, String value) {
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identityHashMap.put(key, value);
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}
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public static void addAllValues(IdentityHashMap<String, String> identityHashMap, Map<String, String> otherMap) {
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identityHashMap.putAll(otherMap);
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}
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public static IdentityHashMap<String, String> createWithSimpleData() {
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IdentityHashMap<String, String> identityHashMap = new IdentityHashMap<>();
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identityHashMap.put("title", "Harry Potter and the Goblet of Fire");
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identityHashMap.put("author", "J. K. Rowling");
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identityHashMap.put("language", "English");
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identityHashMap.put("genre", "Fantasy");
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return identityHashMap;
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}
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}
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@ -0,0 +1,21 @@
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package com.baeldung.map.identity;
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import org.junit.jupiter.api.Test;
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import java.util.IdentityHashMap;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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public class IdentityHashMapDemonstratorUnitTest {
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@Test
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public void givenIdentityHashMap_whenNewObjectWithSameKey_thenAddsAsNewValue() {
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IdentityHashMap<String, String> identityHashMap = IdentityHashMapDemonstrator.createWithSimpleData();
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String newGenreKey = new String("genre");
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identityHashMap.put(newGenreKey, "Drama");
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assertEquals(5, identityHashMap.size());
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assertEquals("Fantasy", identityHashMap.get("genre"));
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assertEquals("Drama", identityHashMap.get(newGenreKey));
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}
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}
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