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BAEL-1736

This commit is contained in:
Ekaterina Galkina 2018-05-12 18:10:42 +05:00
parent daafd33aac
commit 4a81b13958
2 changed files with 302 additions and 0 deletions
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28
core-java-8/src/main/java/com/baeldung/hashtable/Word.java Normal file
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package com.baeldung.hashtable;
public class Word {
private String name;
public Word(String name) {
this.name = name;
}
public String getName() {
return name;
}
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Word))
return false;
Word word = (Word) o;
return word.getName().equals(this.name) ? true : false;
}
public int hashCode() {
return name.hashCode();
}
}

274
core-java-8/src/test/java/com/baeldung/hashtable/HashtableUnitTest.java Normal file
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package com.baeldung.hashtable;
import java.util.ConcurrentModificationException;
import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map;
import static org.junit.Assert.*;
import static org.hamcrest.Matchers.*;
import org.junit.Test;
public class HashtableUnitTest {
@Test
public void whenPutAndGet_thenReturnsValue() {
Hashtable<Word, String> table = new Hashtable<Word, String>();
Word word = new Word("cat");
table.put(word, "an animal");
String definition = table.get(word);
assertEquals("an animal", definition);
definition = table.remove(word);
assertEquals("an animal", definition);
}
@Test
public void whenThesameInstanceOfKey_thenReturnsValue() {
Hashtable<Word, String> table = new Hashtable<Word, String>();
Word word = new Word("cat");
table.put(word, "an animal");
String extracted = table.get(word);
assertEquals("an animal", extracted);
}
@Test
public void whenEqualsOverridden_thenReturnsValue() {
Hashtable<Word, String> table = new Hashtable<Word, String>();
Word word = new Word("cat");
table.put(word, "an animal");
String extracted = table.get(new Word("cat"));
assertEquals("an animal", extracted);
}
@Test(expected = NullPointerException.class)
public void whenNullKey_thenException() {
Hashtable<Word, String> table = new Hashtable<Word, String>();
table.put(null, "an animal");
}
@Test(expected = ConcurrentModificationException.class)
public void whenIterate_thenFailFast() {
Hashtable<Word, String> table = new Hashtable<Word, String>();
table.put(new Word("cat"), "an animal");
table.put(new Word("dog"), "another animal");
Iterator<Word> it = table.keySet().iterator();
System.out.println("iterator created");
table.remove(new Word("dog"));
System.out.println("element removed");
while (it.hasNext()) {
Word key = it.next();
System.out.println(table.get(key));
}
}
@Test
public void whenEnumerate_thenNotFailFast() {
Hashtable<Word, String> table = new Hashtable<Word, String>();
table.put(new Word("1"), "one");
table.put(new Word("2"), "two");
table.put(new Word("3"), "three");
table.put(new Word("4"), "four");
table.put(new Word("5"), "five");
table.put(new Word("6"), "six");
table.put(new Word("7"), "seven");
table.put(new Word("8"), "eight");
Enumeration<Word> enumKey = table.keys();
System.out.println("Enumeration created");
table.remove(new Word("1"));
System.out.println("element removed");
while (enumKey.hasMoreElements()) {
Word key = enumKey.nextElement();
System.out.println(table.get(key));
}
}
@Test
public void whenAddElements_thenIterationOrderUnpredicable() {
Hashtable<Word, String> table = new Hashtable<Word, String>();
table.put(new Word("1"), "one");
table.put(new Word("2"), "two");
table.put(new Word("3"), "three");
table.put(new Word("4"), "four");
table.put(new Word("5"), "five");
table.put(new Word("6"), "six");
table.put(new Word("7"), "seven");
table.put(new Word("8"), "eight");
Iterator<Map.Entry<Word, String>> it = table.entrySet().iterator();
while (it.hasNext()) {
Map.Entry<Word, String> entry = it.next();
System.out.println(entry.getValue());
}
}
@Test
public void whenGetOrDefault_thenDefaultGot() {
Hashtable<Word, String> table = new Hashtable<Word, String>();
table.put(new Word("cat"), "a small domesticated carnivorous mammal");
Word key = new Word("dog");
String definition;
// old way
/* if (table.containsKey(key)) {
definition = table.get(key);
} else {
definition = "not found";
}*/
// new way
definition = table.getOrDefault(key, "not found");
assertThat(definition, is("not found"));
}
@Test
public void whenPutifAbsent_thenNotRewritten() {
Hashtable<Word, String> table = new Hashtable<Word, String>();
table.put(new Word("cat"), "a small domesticated carnivorous mammal");
String definition = "an animal";
// old way
/* if (!table.containsKey(new Word("cat"))) {
table.put(new Word("cat"), definition);
}*/
// new way
table.putIfAbsent(new Word("cat"), definition);
assertThat(table.get(new Word("cat")), is("a small domesticated carnivorous mammal"));
}
@Test
public void whenRemovePair_thenCheckKeyAndValue() {
Hashtable<Word, String> table = new Hashtable<Word, String>();
table.put(new Word("cat"), "a small domesticated carnivorous mammal");
// old way
/* if (table.get(new Word("cat")).equals("an animal")) {
table.remove(new Word("cat"));
}*/
// new way
boolean result = table.remove(new Word("cat"), "an animal");
assertThat(result, is(false));
}
@Test
public void whenReplacePair_thenValueChecked() {
Hashtable<Word, String> table = new Hashtable<Word, String>();
table.put(new Word("cat"), "a small domesticated carnivorous mammal");
String definition = "an animal";
// old way
/* if (table.containsKey(new Word("cat")) && table.get(new Word("cat")).equals("a small domesticated carnivorous mammal")) {
table.put(new Word("cat"), definition);
}*/
// new way
table.replace(new Word("cat"), "a small domesticated carnivorous mammal", definition);
assertThat(table.get(new Word("cat")), is("an animal"));
}
@Test
public void whenKeyIsAbsent_thenNotRewritten() {
Hashtable<Word, String> table = new Hashtable<Word, String>();
table.put(new Word("cat"), "a small domesticated carnivorous mammal");
// old way
/* if (!table.containsKey(cat)) {
String definition = "an animal";// calculate
table.put(new Word("cat"), definition);
}
*/
// new way
table.computeIfAbsent(new Word("cat"), key -> "an animal");
assertThat(table.get(new Word("cat")), is("a small domesticated carnivorous mammal"));
}
@Test
public void whenKeyIsPresent_thenComputeIfPresent() {
Hashtable<Word, String> table = new Hashtable<Word, String>();
table.put(new Word("cat"), "a small domesticated carnivorous mammal");
Word cat = new Word("cat");
// old way
/* if (table.containsKey(cat)) {
String concatination = cat.getName() + " - " + table.get(cat);
table.put(cat, concatination);
}*/
// new way
table.computeIfPresent(cat, (key, value) -> key.getName() + " - " + value);
assertThat(table.get(cat), is("cat - a small domesticated carnivorous mammal"));
}
@Test
public void whenCompute_thenForAllKeys() {
Hashtable<String, Integer> table = new Hashtable<String, Integer>();
String[] animals = { "cat", "dog", "dog", "cat", "bird", "mouse", "mouse" };
for (String animal : animals) {
table.compute(animal, (key, value) -> (value == null ? Integer.valueOf(1) : Integer.valueOf(value) + 1));
}
assertThat(table.values(), hasItems(2, 2, 2, 1));
}
@Test
public void whenInsteadOfCompute_thenMerge() {
Hashtable<String, Integer> table = new Hashtable<String, Integer>();
String[] animals = { "cat", "dog", "dog", "cat", "bird", "mouse", "mouse" };
for (String animal : animals) {
table.merge(animal, 1, (oldValue, value) -> (oldValue + value));
}
assertThat(table.values(), hasItems(2, 2, 2, 1));
}
@Test
public void whenForeach_thenIterate() {
Hashtable<Word, String> table = new Hashtable<Word, String>();
table.put(new Word("cat"), "a small domesticated carnivorous mammal");
table.put(new Word("dog"), "another animal");
table.forEach((k, v) -> System.out.println(k.getName() + " - " + v)
);
}
@Test
public void whenReplaceall_thenNoIterationNeeded() {
Hashtable<Word, String> table = new Hashtable<Word, String>();
table.put(new Word("cat"), "a small domesticated carnivorous mammal");
table.put(new Word("dog"), "another animal");
table.replaceAll((k, v) -> k.getName() + " - " + v);
assertThat(table.values(), hasItems("cat - a small domesticated carnivorous mammal", "dog - another animal"));
}
}