José Carlos Valero Sánchez
GitHub
commit
d2ee505ad7
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package com.baeldung.hashtable;
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public class Word {
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private String name;
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public Word(String name) {
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this.name = name;
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}
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public String getName() {
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return name;
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}
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public boolean equals(Object o) {
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if (o == this)
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return true;
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if (!(o instanceof Word))
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return false;
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Word word = (Word) o;
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return word.getName().equals(this.name) ? true : false;
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}
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public int hashCode() {
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return name.hashCode();
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}
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}
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package com.baeldung.hashtable;
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import java.util.ConcurrentModificationException;
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import java.util.Enumeration;
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import java.util.Hashtable;
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import java.util.Iterator;
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import java.util.Map;
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import static org.junit.Assert.*;
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import static org.hamcrest.Matchers.*;
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import org.junit.Test;
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public class HashtableUnitTest {
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@Test
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public void whenPutAndGet_thenReturnsValue() {
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Hashtable<Word, String> table = new Hashtable<Word, String>();
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Word word = new Word("cat");
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table.put(word, "an animal");
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String definition = table.get(word);
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assertEquals("an animal", definition);
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definition = table.remove(word);
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assertEquals("an animal", definition);
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}
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@Test
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public void whenThesameInstanceOfKey_thenReturnsValue() {
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Hashtable<Word, String> table = new Hashtable<Word, String>();
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Word word = new Word("cat");
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table.put(word, "an animal");
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String extracted = table.get(word);
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assertEquals("an animal", extracted);
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}
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@Test
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public void whenEqualsOverridden_thenReturnsValue() {
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Hashtable<Word, String> table = new Hashtable<Word, String>();
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Word word = new Word("cat");
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table.put(word, "an animal");
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String extracted = table.get(new Word("cat"));
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assertEquals("an animal", extracted);
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}
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@Test(expected = NullPointerException.class)
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public void whenNullKey_thenException() {
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Hashtable<Word, String> table = new Hashtable<Word, String>();
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table.put(null, "an animal");
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}
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@Test(expected = ConcurrentModificationException.class)
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public void whenIterate_thenFailFast() {
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Hashtable<Word, String> table = new Hashtable<Word, String>();
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table.put(new Word("cat"), "an animal");
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table.put(new Word("dog"), "another animal");
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Iterator<Word> it = table.keySet().iterator();
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System.out.println("iterator created");
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table.remove(new Word("dog"));
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System.out.println("element removed");
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while (it.hasNext()) {
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Word key = it.next();
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System.out.println(table.get(key));
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}
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}
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@Test
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public void whenEnumerate_thenNotFailFast() {
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Hashtable<Word, String> table = new Hashtable<Word, String>();
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table.put(new Word("1"), "one");
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table.put(new Word("2"), "two");
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table.put(new Word("3"), "three");
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table.put(new Word("4"), "four");
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table.put(new Word("5"), "five");
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table.put(new Word("6"), "six");
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table.put(new Word("7"), "seven");
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table.put(new Word("8"), "eight");
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Enumeration<Word> enumKey = table.keys();
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System.out.println("Enumeration created");
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table.remove(new Word("1"));
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System.out.println("element removed");
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while (enumKey.hasMoreElements()) {
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Word key = enumKey.nextElement();
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System.out.println(table.get(key));
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}
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}
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@Test
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public void whenAddElements_thenIterationOrderUnpredicable() {
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Hashtable<Word, String> table = new Hashtable<Word, String>();
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table.put(new Word("1"), "one");
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table.put(new Word("2"), "two");
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table.put(new Word("3"), "three");
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table.put(new Word("4"), "four");
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table.put(new Word("5"), "five");
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table.put(new Word("6"), "six");
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table.put(new Word("7"), "seven");
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table.put(new Word("8"), "eight");
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Iterator<Map.Entry<Word, String>> it = table.entrySet().iterator();
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while (it.hasNext()) {
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Map.Entry<Word, String> entry = it.next();
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System.out.println(entry.getValue());
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}
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}
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@Test
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public void whenGetOrDefault_thenDefaultGot() {
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Hashtable<Word, String> table = new Hashtable<Word, String>();
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table.put(new Word("cat"), "a small domesticated carnivorous mammal");
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Word key = new Word("dog");
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String definition;
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// old way
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/* if (table.containsKey(key)) {
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definition = table.get(key);
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} else {
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definition = "not found";
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}*/
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// new way
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definition = table.getOrDefault(key, "not found");
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assertThat(definition, is("not found"));
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}
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@Test
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public void whenPutifAbsent_thenNotRewritten() {
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Hashtable<Word, String> table = new Hashtable<Word, String>();
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table.put(new Word("cat"), "a small domesticated carnivorous mammal");
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String definition = "an animal";
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// old way
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/* if (!table.containsKey(new Word("cat"))) {
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table.put(new Word("cat"), definition);
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}*/
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// new way
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table.putIfAbsent(new Word("cat"), definition);
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assertThat(table.get(new Word("cat")), is("a small domesticated carnivorous mammal"));
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}
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@Test
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public void whenRemovePair_thenCheckKeyAndValue() {
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Hashtable<Word, String> table = new Hashtable<Word, String>();
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table.put(new Word("cat"), "a small domesticated carnivorous mammal");
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// old way
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/* if (table.get(new Word("cat")).equals("an animal")) {
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table.remove(new Word("cat"));
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}*/
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// new way
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boolean result = table.remove(new Word("cat"), "an animal");
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assertThat(result, is(false));
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}
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@Test
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public void whenReplacePair_thenValueChecked() {
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Hashtable<Word, String> table = new Hashtable<Word, String>();
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table.put(new Word("cat"), "a small domesticated carnivorous mammal");
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String definition = "an animal";
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// old way
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/* if (table.containsKey(new Word("cat")) && table.get(new Word("cat")).equals("a small domesticated carnivorous mammal")) {
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table.put(new Word("cat"), definition);
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}*/
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// new way
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table.replace(new Word("cat"), "a small domesticated carnivorous mammal", definition);
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assertThat(table.get(new Word("cat")), is("an animal"));
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}
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@Test
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public void whenKeyIsAbsent_thenNotRewritten() {
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Hashtable<Word, String> table = new Hashtable<Word, String>();
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table.put(new Word("cat"), "a small domesticated carnivorous mammal");
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// old way
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/* if (!table.containsKey(cat)) {
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String definition = "an animal";// calculate
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table.put(new Word("cat"), definition);
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}
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*/
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// new way
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table.computeIfAbsent(new Word("cat"), key -> "an animal");
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assertThat(table.get(new Word("cat")), is("a small domesticated carnivorous mammal"));
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}
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@Test
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public void whenKeyIsPresent_thenComputeIfPresent() {
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Hashtable<Word, String> table = new Hashtable<Word, String>();
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table.put(new Word("cat"), "a small domesticated carnivorous mammal");
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Word cat = new Word("cat");
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// old way
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/* if (table.containsKey(cat)) {
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String concatination = cat.getName() + " - " + table.get(cat);
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table.put(cat, concatination);
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}*/
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// new way
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table.computeIfPresent(cat, (key, value) -> key.getName() + " - " + value);
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assertThat(table.get(cat), is("cat - a small domesticated carnivorous mammal"));
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}
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@Test
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public void whenCompute_thenForAllKeys() {
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Hashtable<String, Integer> table = new Hashtable<String, Integer>();
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String[] animals = { "cat", "dog", "dog", "cat", "bird", "mouse", "mouse" };
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for (String animal : animals) {
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table.compute(animal, (key, value) -> (value == null ? Integer.valueOf(1) : Integer.valueOf(value) + 1));
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}
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assertThat(table.values(), hasItems(2, 2, 2, 1));
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}
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@Test
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public void whenInsteadOfCompute_thenMerge() {
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Hashtable<String, Integer> table = new Hashtable<String, Integer>();
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String[] animals = { "cat", "dog", "dog", "cat", "bird", "mouse", "mouse" };
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for (String animal : animals) {
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table.merge(animal, 1, (oldValue, value) -> (oldValue + value));
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}
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assertThat(table.values(), hasItems(2, 2, 2, 1));
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}
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@Test
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public void whenForeach_thenIterate() {
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Hashtable<Word, String> table = new Hashtable<Word, String>();
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table.put(new Word("cat"), "a small domesticated carnivorous mammal");
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table.put(new Word("dog"), "another animal");
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table.forEach((k, v) -> System.out.println(k.getName() + " - " + v)
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);
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}
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@Test
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public void whenReplaceall_thenNoIterationNeeded() {
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Hashtable<Word, String> table = new Hashtable<Word, String>();
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table.put(new Word("cat"), "a small domesticated carnivorous mammal");
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table.put(new Word("dog"), "another animal");
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table.replaceAll((k, v) -> k.getName() + " - " + v);
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assertThat(table.values(), hasItems("cat - a small domesticated carnivorous mammal", "dog - another animal"));
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}
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}
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