Java ArrayList Class - Java 147

Java ArrayList Class – Java 147

Java ArrayList Class

實作集合框架的 List 接口,可以隨時增加或刪除元素,使用動態陣列來存儲元素,實現可調整大小陣列的功能,ArrayList Class 介紹常見的 contains 、 indexOf 、 sort 、 stream 、 subList 等方法,了解陣列列表的不同操作和方法,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
       |               +- list
       |                   +- arraylist
       |                       +- ArrayListClassTest.java  

單元測試

ArrayList Class Java 提供檢查包含、搜索指定、排序、串流操作列表中的元素。

contains

建立一個 ArrayList ,增加三個元素,檢查包含指定的元素。

	@Test
	public void contains() {
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");

		boolean contains = list.contains("Apple");
		System.out.println(contains);
		assertTrue(contains);

		contains = list.contains("Grape");
		System.out.println(contains);
		assertFalse(contains);
	}
true
false

containsAll

ArrayList Class Java 建立一個 ArrayList ,內有三個元素,,檢查包含所有指定的元素。

	@Test
	public void containsAll() {
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");

		List<String> list2 = new ArrayList<>();
		list2.add("Apple");
		list2.add("Banana");

		boolean contains = list.containsAll(list2);
		System.out.println(contains);
		assertTrue(contains);

		contains = list2.containsAll(list);
		System.out.println(contains);
		assertFalse(contains);
	}
true
false

indexOf

ArrayList Class Java 建立一個 ArrayList ,內有三個元素,搜索指定元素,傳回索引。

	@Test
	public void indexOf() {
		int expected = 1;
		List<String> list = new ArrayList<String>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");

		int index = list.indexOf("Banana");
		System.out.println(index);
		assertEquals(expected, index);

		index = list.indexOf("Grape");
		System.out.println(index);
		assertEquals(-1, index);
	}
1
-1

lastIndexOf

ArrayList Class Java 建立一個 ArrayList ,從最後搜索指定元素,傳回索引。

	@Test
	public void lastIndexOf() {
		int expected = 3;
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");
		list.add("Apple");

		int index = list.lastIndexOf("Apple");
		System.out.println(index);
		assertEquals(expected, index);

		index = list.indexOf("Grape");
		System.out.println(index);
		assertEquals(-1, index);
	}
3
-1

sort

ArrayList Class in Java 建立一個 ArrayList ,內有三個元素,排序元素。

	@Test
	public void sort() {
		List<String> list = new ArrayList<>();
		list.add("Banana");
		list.add("Apple");
		list.add("Cherry");
		list.sort(Comparator.naturalOrder());
		System.out.println(list);

		list.add("Grape");
		list.sort(Comparator.reverseOrder());
		System.out.println(list);
	}	
[Apple, Banana, Cherry]
[Grape, Cherry, Banana, Apple]

stream

ArrayList Class in Java 建立一個 ArrayList ,內有三個元素,執行串流,取得長度小於 6 的元素。

	@Test
	public void stream() {
		int expectedSize = 1;
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");
		list = list.stream().filter(e -> e.length() < 6).collect(Collectors.toList());
		System.out.println(list);
		assertEquals(expectedSize, list.size());
	}
[Apple]

parallelStream

ArrayList Class in Java 建立一個 ArrayList ,內有三個元素,並行執行串流。

	@Test
	public void parallelStream() {
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");
		list.parallelStream().forEach(System.out::println);
		System.out.println("----------");
		list.parallelStream().forEachOrdered(System.out::println);
	}
Banana
Cherry
Apple
----------
Apple
Banana
Cherry

subList

Java ArrayList Class Eexample 建立一個 ArrayList ,內有三個元素,建立指定位置的子列表 。

	@Test
	public void subList() {
		int expectedSize = 2;
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");
		System.out.println(list);
		List<String> list2 = list.subList(0, 2);
		System.out.println(list2);

		assertEquals(expectedSize, list2.size());
	}
[Apple, Banana, Cherry]
[Apple, Banana]

replaceAll

Java ArrayList Class Eexample 建立一個 ArrayList ,內有三個元素,替換所有元素 。

	@Test
	public void replaceAll() {
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");
		list.replaceAll(e -> e.toUpperCase());
		System.out.println(list);
	}
[APPLE, BANANA, CHERRY]

retainAll

Java ArrayList Class Eexample 建立兩個 ArrayList ,內各有三個元素,只保留相同元素 。

	@Test
	public void retainAll() {
		int expectedSize = 1;
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");

		List<String> list2 = new ArrayList<>();
		list2.add("Apple");
		list2.add("Lemon");
		list2.add("Mango");

		list.retainAll(list2);
		System.out.println(list);
		assertEquals(expectedSize, list.size());
	}
[Apple]

ArrayListClassTest.java

ArrayList Class in Java 新增單元測試,驗證是否符合預期。

package org.ruoxue.java_147.list.arraylist;

import static org.junit.Assert.*;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

import org.junit.Test;

public class ArrayListClassTest {

	@Test
	public void contains() {
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");

		boolean contains = list.contains("Apple");
		System.out.println(contains);
		assertTrue(contains);

		contains = list.contains("Grape");
		System.out.println(contains);
		assertFalse(contains);
	}

	@Test
	public void containsAll() {
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");

		List<String> list2 = new ArrayList<>();
		list2.add("Apple");
		list2.add("Banana");

		boolean contains = list.containsAll(list2);
		System.out.println(contains);
		assertTrue(contains);

		contains = list2.containsAll(list);
		System.out.println(contains);
		assertFalse(contains);
	}

	@Test
	public void indexOf() {
		int expected = 1;
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");

		int index = list.indexOf("Banana");
		System.out.println(index);
		assertEquals(expected, index);

		index = list.indexOf("Grape");
		System.out.println(index);
		assertEquals(-1, index);
	}

	@Test
	public void lastIndexOf() {
		int expected = 3;
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");
		list.add("Apple");

		int index = list.lastIndexOf("Apple");
		System.out.println(index);
		assertEquals(expected, index);

		index = list.indexOf("Grape");
		System.out.println(index);
		assertEquals(-1, index);
	}

	@Test
	public void sort() {
		List<String> list = new ArrayList<>();
		list.add("Banana");
		list.add("Apple");
		list.add("Cherry");
		list.sort(Comparator.naturalOrder());
		System.out.println(list);

		list.add("Grape");
		list.sort(Comparator.reverseOrder());
		System.out.println(list);
	}

	@Test
	public void stream() {
		int expectedSize = 1;
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");
		list = list.stream().filter(e -> e.length() < 6).collect(Collectors.toList());
		System.out.println(list);
		assertEquals(expectedSize, list.size());
	}

	@Test
	public void parallelStream() {
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");
		list.parallelStream().forEach(System.out::println);
		System.out.println("----------");
		list.parallelStream().forEachOrdered(System.out::println);
	}

	@Test
	public void subList() {
		int expectedSize = 2;
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");
		System.out.println(list);
		List<String> list2 = list.subList(0, 2);
		System.out.println(list2);

		assertEquals(expectedSize, list2.size());
	}

	@Test
	public void replaceAll() {
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");
		list.replaceAll(e -> e.toUpperCase());
		System.out.println(list);
	}

	@Test
	public void retainAll() {
		int expectedSize = 1;
		List<String> list = new ArrayList<>();
		list.add("Apple");
		list.add("Banana");
		list.add("Cherry");

		List<String> list2 = new ArrayList<>();
		list2.add("Apple");
		list2.add("Lemon");
		list2.add("Mango");

		list.retainAll(list2);
		System.out.println(list);
		assertEquals(expectedSize, list.size());
	}
}

心得分享

Java ArrayList Class Eexample 操作比 LinkedList 慢一點,因為如果從陣列列表中刪除任何元素,則需要進行大量移位,提供了幾種 ArrayList 常見方法的操作範例, ArrayList Class in Java 在應用上相當廣泛,熟悉這些方法的操作,能夠提高開發效率,節省維護上的成本。

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