Table of Contents
ToggleHashSet in Java with Examples
不會依新增順序保持排序,自動調整其容量,是一個非同步的操作, HashSet in Java 介紹常見的 forEach 、 iterator 、 spliterator 、 trySplit 等方法,本篇增加了範例,並透過單元測試來驗證產出結果。
檔案目錄
./
+- src
+- test
| +- org
| +- ruoxue
| +- java_147
| +- set
| +- hashset
| +- HashSetWithExamplesTest.java
單元測試
HashSet Java 提供循環訪問、轉成陣列等操作 Set 中的元素。
forEach
建立一個 HashSet ,內有三個元素,迴圈取得元素。
@Test
public void forEach() {
Set<String> set = new HashSet<>();
set.add("Longan");
set.add("Tomato");
set.add("Pear");
set.forEach(e -> System.out.println(e));
}
Pear
Longan
Tomato
forEachRemaining
HashSet Java 建立一個 HashSet ,內有三個元素,迴圈取得剩餘元素。
@Test
public void forEachRemaining() {
Set<String> set = new HashSet<>();
set.add("Longan");
set.add("Tomato");
set.add("Pear");
Iterator<String> it = set.iterator();
int i = 0;
while (it.hasNext()) {
System.out.println(it.next());
if (i == 1) {
break;
}
i++;
}
System.out.println("----------");
it.forEachRemaining(e -> {
System.out.println(e);
});
}
Pear
Longan
----------
Tomato
iterator
HashSet Java 建立一個 HashSet ,內有三個元素,迴圈取得元素。
@Test
public void iterator() {
Set<String> set = new HashSet<>();
set.add("Longan");
set.add("Tomato");
set.add("Pear");
Iterator<String> it = set.iterator();
while (it.hasNext()) {
System.out.println(it.next());
}
}
Pear
Longan
Tomato
spliterator
Java HashSet 建立一個 HashSet ,內有三個元素,使用 spliterator 取得元素,等同於 iterator.hasNext 和 iterator.next。
@Test
public void spliterator() {
Set<String> set = new HashSet<>();
set.add("Longan");
set.add("Tomato");
set.add("Pear");
Spliterator<String> sit = set.spliterator();
sit.tryAdvance(e -> System.out.println(e));
System.out.println("----------");
sit.forEachRemaining(e -> System.out.println(e));
System.out.println("----------");
sit = set.spliterator();
while (sit.tryAdvance(e -> System.out.println(e))) {
}
}
Pear
----------
Longan
Tomato
----------
Pear
Longan
Tomato
trySplit
Java HashSet 建立一個 HashSet ,內有三個元素,使用 spliterator 取得元素,trySplit 將目前的拆分器分為兩個新的拆分器並行處理。
@Test
public void trySplit() {
Set<String> set = new HashSet<>();
set.add("Longan");
set.add("Tomato");
set.add("Pear");
Spliterator<String> sit = set.spliterator();
Spliterator<String> sit2 = sit.trySplit();
System.out.println(sit.getExactSizeIfKnown());
sit.forEachRemaining(e -> System.out.println(e));
System.out.println("----------");
System.out.println(sit2.getExactSizeIfKnown());
sit2.forEachRemaining(e -> System.out.println(e));
}
-1
Longan
Tomato
----------
-1
Pear
toArray
Java HashSet 建立一個 HashSet ,內有三個元素,轉換成 String 陣列。
@Test
public void toArray() {
int expectedSize = 3;
Set<String> set = new HashSet<>();
set.add("Longan");
set.add("Tomato");
set.add("Pear");
String[] array = new String[set.size()];
set.toArray(array);
for (String e : array) {
System.out.println(e);
}
assertEquals(expectedSize, array.length);
}
Pear
Longan
Tomato
streamToArray
Java HashSet 建立一個 HashSet ,內有三個元素,使用 Stream ,轉換成 String 陣列。
@Test
public void streamToArray() {
int expectedSize = 3;
Set<String> set = new HashSet<>();
set.add("Longan");
set.add("Tomato");
set.add("Pear");
String[] array = set.stream().toArray(String[]::new);
for (String e : array) {
System.out.println(e);
}
assertEquals(expectedSize, array.length);
}
Pear
Longan
Tomato
HashSetWithExamplesTest.java
Java HashSet 新增單元測試,驗證是否符合預期。
package org.ruoxue.java_147.set.hashset;
import static org.junit.Assert.*;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import java.util.Spliterator;
import org.junit.Test;
public class HashSetWithExamplesTest {
@Test
public void forEach() {
Set<String> set = new HashSet<>();
set.add("Longan");
set.add("Tomato");
set.add("Pear");
set.forEach(e -> System.out.println(e));
}
@Test
public void forEachRemaining() {
Set<String> set = new HashSet<>();
set.add("Longan");
set.add("Tomato");
set.add("Pear");
Iterator<String> it = set.iterator();
int i = 0;
while (it.hasNext()) {
System.out.println(it.next());
if (i == 1) {
break;
}
i++;
}
System.out.println("----------");
it.forEachRemaining(e -> {
System.out.println(e);
});
}
@Test
public void iterator() {
Set<String> set = new HashSet<>();
set.add("Longan");
set.add("Tomato");
set.add("Pear");
Iterator<String> it = set.iterator();
while (it.hasNext()) {
System.out.println(it.next());
}
}
@Test
public void spliterator() {
Set<String> set = new HashSet<>();
set.add("Longan");
set.add("Tomato");
set.add("Pear");
Spliterator<String> sit = set.spliterator();
sit.tryAdvance(e -> System.out.println(e));
System.out.println("----------");
sit.forEachRemaining(e -> System.out.println(e));
System.out.println("----------");
sit = set.spliterator();
while (sit.tryAdvance(e -> System.out.println(e))) {
}
}
@Test
public void trySplit() {
Set<String> set = new HashSet<>();
set.add("Longan");
set.add("Tomato");
set.add("Pear");
Spliterator<String> sit = set.spliterator();
Spliterator<String> sit2 = sit.trySplit();
System.out.println(sit.getExactSizeIfKnown());
sit.forEachRemaining(e -> System.out.println(e));
System.out.println("----------");
System.out.println(sit2.getExactSizeIfKnown());
sit2.forEachRemaining(e -> System.out.println(e));
}
@Test
public void toArray() {
int expectedSize = 3;
Set<String> set = new HashSet<>();
set.add("Longan");
set.add("Tomato");
set.add("Pear");
String[] array = new String[set.size()];
set.toArray(array);
for (String e : array) {
System.out.println(e);
}
assertEquals(expectedSize, array.length);
}
@Test
public void streamToArray() {
int expectedSize = 3;
Set<String> set = new HashSet<>();
set.add("Longan");
set.add("Tomato");
set.add("Pear");
String[] array = set.stream().toArray(String[]::new);
for (String e : array) {
System.out.println(e);
}
assertEquals(expectedSize, array.length);
}
}
心得分享
Java HashSet Example 提供了幾種 HashSet 常見方法的操作範例,在應用上相當廣泛,熟悉 Java HashSet 這些方法的操作,可以快速撰寫程式,降低錯誤率,再輔以單元測試驗證,建置高效穩定的服務或系統。