Table of Contents

Java Remove Elements From Map

移除條件相符合的元素，提供幾種 HashMap 刪除元素的方法，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
       |               +- Map
       |                   +- RemoveElementsFromMapTest.java

單元測試

Remove an Element from HashMap 移除條件相符合的元素。

removeByKey

建立一個 HashMap ，內有三個元素，移除條件 key 相符合的元素。

	@Test
	public void removeByKey() {
		int expectedSize = 2;
		Integer expectedValue = 1;
		Map<String, Integer> map = new HashMap<String, Integer>();
		map.put("Grape", 1);
		map.put("Kiwifruit", 2);
		map.put("Lemon", 3);
		Integer removed = map.remove("Grape");

		System.out.println(removed);
		assertEquals(expectedValue, removed);
		System.out.println(map);
		assertEquals(expectedSize, map.size());
	}

1
{Kiwifruit=2, Lemon=3}

removeByKeyValue

建立一個 HashMap ，內有三個元素，移除條件 key 、 value 相符合的元素。

	@Test
	public void removeByKeyValue() {
		int expectedSize = 2;
		Map<String, Integer> map = new HashMap<String, Integer>();
		map.put("Grape", 1);
		map.put("Kiwifruit", 2);
		map.put("Lemon", 3);
		boolean removed = map.remove("Lemon", 3);

		System.out.println(removed);
		assertTrue(removed);
		System.out.println(map);
		assertEquals(expectedSize, map.size());

		removed = map.remove("Lemon", 10);
		System.out.println(removed);
		assertFalse(removed);
		System.out.println(map);
		assertEquals(expectedSize, map.size());
	}

true
{Grape=1, Kiwifruit=2}
false
{Grape=1, Kiwifruit=2}

keyIteratorRemove

建立一個 HashMap ，內有三個元素，使用 keySet iterator ，在迴圈內移除條件相符合的元素。

	@Test
	public void keyIteratorRemove() {
		int expectedSize = 2;
		Map<String, Integer> map = new HashMap<String, Integer>();
		map.put("Grape", 1);
		map.put("Kiwifruit", 2);
		map.put("Lemon", 3);
		Iterator<String> it = map.keySet().iterator();
		while (it.hasNext()) {
			String e = it.next();
			if (Objects.equal("Kiwifruit", e)) {
				it.remove();
			}
		}
		System.out.println(map);
		assertEquals(expectedSize, map.size());
	}

{Grape=1, Lemon=3}

valuesIteratorRemove

建立一個 HashMap ，內有三個元素，使用 values iterator ，在迴圈內移除條件相符合的元素。

	@Test
	public void valuesIteratorRemove() {
		int expectedSize = 2;
		Map<String, Integer> map = new HashMap<String, Integer>();
		map.put("Grape", 1);
		map.put("Kiwifruit", 2);
		map.put("Lemon", 3);
		Iterator<Integer> it = map.values().iterator();
		while (it.hasNext()) {
			Integer e = it.next();
			if (Objects.equal(3, e)) {
				it.remove();
			}
		}
		System.out.println(map);
		assertEquals(expectedSize, map.size());
	}

{Grape=1, Kiwifruit=2}

remove

建立一個 HashMap ，內有三個元素，把條件相符合的元素放入新的 Map ，然後新的 Map 迴圈內，移除舊的 Map 條件相符合的元素。

	@Test
	public void remove() {
		int expectedSize = 2;
		Map<String, Integer> map = new HashMap<String, Integer>();
		map.put("Grape", 1);
		map.put("Kiwifruit", 2);
		map.put("Lemon", 3);
		List<String> willRemove = new ArrayList<>();
		for (Map.Entry<String, Integer> e : map.entrySet()) {
			String key = e.getKey();
			if ("Grape".equals(key)) {
				willRemove.add(key);
			}
		}
		for (String e : willRemove) {
			map.remove(e);
		}
		System.out.println(map);
		assertEquals(expectedSize, map.size());
	}

{Kiwifruit=2, Lemon=3}

RemoveElementsFromMapTest.java

Java HashMap Remove 新增單元測試，驗證是否符合預期。

package org.ruoxue.java_147.map;

import static org.junit.Assert.*;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import java.util.Iterator;
import java.util.List;

import org.junit.Test;

import com.google.common.base.Objects;

public class RemoveElementsFromMapTest {

	public RemoveElementsFromMapTest() {

	}

	@Test
	public void removeByKey() {
		int expectedSize = 2;
		Integer expectedValue = 1;
		Map<String, Integer> map = new HashMap<String, Integer>();
		map.put("Grape", 1);
		map.put("Kiwifruit", 2);
		map.put("Lemon", 3);
		Integer removed = map.remove("Grape");

		System.out.println(removed);
		assertEquals(expectedValue, removed);
		System.out.println(map);
		assertEquals(expectedSize, map.size());
	}

	@Test
	public void removeByKeyValue() {
		int expectedSize = 2;
		Map<String, Integer> map = new HashMap<String, Integer>();
		map.put("Grape", 1);
		map.put("Kiwifruit", 2);
		map.put("Lemon", 3);
		boolean removed = map.remove("Lemon", 3);

		System.out.println(removed);
		assertTrue(removed);
		System.out.println(map);
		assertEquals(expectedSize, map.size());

		removed = map.remove("Lemon", 10);
		System.out.println(removed);
		assertFalse(removed);
		System.out.println(map);
		assertEquals(expectedSize, map.size());
	}

	@Test
	public void keyIteratorRemove() {
		int expectedSize = 2;
		Map<String, Integer> map = new HashMap<String, Integer>();
		map.put("Grape", 1);
		map.put("Kiwifruit", 2);
		map.put("Lemon", 3);
		Iterator<String> it = map.keySet().iterator();
		while (it.hasNext()) {
			String e = it.next();
			if (Objects.equal("Kiwifruit", e)) {
				it.remove();
			}
		}
		System.out.println(map);
		assertEquals(expectedSize, map.size());
	}

	@Test
	public void valuesIteratorRemove() {
		int expectedSize = 2;
		Map<String, Integer> map = new HashMap<String, Integer>();
		map.put("Grape", 1);
		map.put("Kiwifruit", 2);
		map.put("Lemon", 3);
		Iterator<Integer> it = map.values().iterator();
		while (it.hasNext()) {
			Integer e = it.next();
			if (Objects.equal(3, e)) {
				it.remove();
			}
		}
		System.out.println(map);
		assertEquals(expectedSize, map.size());
	}
	
	@Test
	public void remove() {
		int expectedSize = 2;
		Map<String, Integer> map = new HashMap<String, Integer>();
		map.put("Grape", 1);
		map.put("Kiwifruit", 2);
		map.put("Lemon", 3);
		List<String> willRemove = new ArrayList<>();
		for (Map.Entry<String, Integer> e : map.entrySet()) {
			String key = e.getKey();
			if ("Grape".equals(key)) {
				willRemove.add(key);
			}
		}
		for (String e : willRemove) {
			map.remove(e);
		}
		System.out.println(map);
		assertEquals(expectedSize, map.size());
	}
}