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List sort in Java with Examples - Java 147

List sort in Java with Examples – Java 147

List sort in Java with Examples

調用 List sort 方法，採用預設或自定義比較器，對集合進行排序，比較器需實作 Comparator compare 方法，比較兩個物件並傳回一個整數， Java List Sort with Examples 利用傳統方式或 Lambda 表達式進行實作，本篇增加了範例，並透過單元測試來驗證產出結果。

default void sort(Comparator<? super E> c) {
}

檔案目錄

./
   +- src
       +- test
       |   +- org
       |       +- ruoxue
       |           +- java_147
       |               +- list
       |                   +- sort
       |                       +- ListSortWithExamplesTest.java

單元測試

Java List Sort 提供不同類型的資料進行排序，使用自定義比較器，排序集合中的元素。

sort

Java List Sort 建立一個 List ，增加三個元素，使用 List sort 方法，依照預設比較器，由小到大，升序對集合進行排序。

	@Test
	public void sort() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d);
		System.out.println(list);

		list.sort(null);
		System.out.println(list);
		assertThat(list).containsExactly(-1d, 3d, Double.MAX_VALUE);
	}
[1.7976931348623157E308, -1.0, 3.0]
[-1.0, 3.0, 1.7976931348623157E308]

sortWithReverseOrder

Java List Sort 建立一個 List ，增加三個元素，使用 List sort 方法，依照預設反向比較器，由小到大，升序對集合進行排序。

	@Test
	public void sortWithReverseOrder() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d);
		System.out.println(list);

		list.sort(Comparator.reverseOrder());
		System.out.println(list);
		assertThat(list).containsExactly(Double.MAX_VALUE, 3d, -1d);
	}
[1.7976931348623157E308, -1.0, 3.0]
[1.7976931348623157E308, 3.0, -1.0]

sortWithComparator

Java List Sort 建立一個 List ，增加三個元素，使用 List sort 方法，依照自定義比較器，由小到大，升序對集合進行排序。

	@Test
	public void sortWithComparator() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d);
		System.out.println(list);

		list.sort((i1, i2) -> Double.compare(i1, i2));
		System.out.println(list);
		assertThat(list).containsExactly(-1d, 3d, Double.MAX_VALUE);
	}
[1.7976931348623157E308, -1.0, 3.0]
[-1.0, 3.0, 1.7976931348623157E308]

sortWithComparing

List Sort Java 建立一個 List ，增加三個元素，使用 List sort 方法，依照自定義比較器，由小到大，升序對集合進行排序。

	@Test
	public void sortWithComparing() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d);
		System.out.println(list);

		list.sort(Comparator.comparing(Double::doubleValue));
		System.out.println(list);
		assertThat(list).containsExactly(-1d, 3d, Double.MAX_VALUE);
	}
[1.7976931348623157E308, -1.0, 3.0]
[-1.0, 3.0, 1.7976931348623157E308]

sortWithComparingDouble

List Sort Java 建立一個 List ，增加三個元素，使用 List sort 方法，依照自定義比較器，由小到大，升序對集合進行排序。

	@Test
	public void sortWithComparingDouble() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d);
		System.out.println(list);

		list.sort(Comparator.comparingDouble(d -> d));
		System.out.println(list);
		assertThat(list).containsExactly(-1d, 3d, Double.MAX_VALUE);
	}
[1.7976931348623157E308, -1.0, 3.0]
[-1.0, 3.0, 1.7976931348623157E308]

sortWithMultipleConditions

List Sort Java 建立一個 List ，增加三個元素，使用 List sort 方法，依照多個自定義比較器，由小到大，升序對集合進行排序。

	protected static Comparator<Double> valueComparator = new Comparator<Double>() {
		@Override
		public int compare(Double i1, Double i2) {
			return Double.compare(i1, i2);
		}
	};

	protected static Comparator<Double> lengthComparator = (i1, i2) -> Double.compare(String.valueOf(i1).length(),
			String.valueOf(i2).length());

	@Test
	public void sortWithMultipleConditions() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d);
		System.out.println(list);

		list.sort(valueComparator.thenComparing(lengthComparator));
		System.out.println(list);
		assertThat(list).containsExactly(-1d, 3d, Double.MAX_VALUE);
	}
[1.7976931348623157E308, -1.0, 3.0]
[-1.0, 3.0, 1.7976931348623157E308]

sortWithNull

建立一個 List ，增加三個元素及一個 null 元素，使用 List sort 方法，依照自定義比較器， null 元素放在第一個，由小到大，升序對集合進行排序。

	@Test
	public void sortWithNull() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d, null);
		System.out.println(list);

		list.sort((s1, s2) -> {
			if (s1 == null) {
				return s2 == null ? 0 : -1;
			} else if (s2 == null) {
				return 1;
			}
			return s1.compareTo(s2);
		});
		System.out.println(list);
		assertThat(list).containsExactly(null, -1d, 3d, Double.MAX_VALUE);
	}
[1.7976931348623157E308, -1.0, 3.0, null]
[null, -1.0, 3.0, 1.7976931348623157E308]

sortWithNullsFirst

建立一個 List ，增加三個元素及一個 null 元素，使用 List sort 方法，依照 nullsFirst 比較器， null 元素放在第一個，由小到大，升序對集合進行排序。

	@Test
	public void sortWithNullsFirst() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d, null);
		System.out.println(list);

		list.sort(Comparator.nullsFirst(Comparator.comparing(s -> s)));
		System.out.println(list);
		assertThat(list).containsExactly(null, -1d, 3d, Double.MAX_VALUE);
	}
[1.7976931348623157E308, -1.0, 3.0, null]
[null, -1.0, 3.0, 1.7976931348623157E308]

sortWithNullsLast

建立一個 List ，增加三個元素及一個 null 元素，使用 List sort 方法，依照 nullsLast 比較器， null 元素放在最後個，由小到大，升序對集合進行排序。

	@Test
	public void sortWithNullsLast() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d, null);
		System.out.println(list);

		list.sort(Comparator.nullsLast(Comparator.comparing(s -> s)));
		System.out.println(list);
		assertThat(list).containsExactly(-1d, 3d, Double.MAX_VALUE, null);
	}
[1.7976931348623157E308, -1.0, 3.0, null]
[-1.0, 3.0, 1.7976931348623157E308, null]

ListSortWithExamplesTest.java

List Sort Java 新增單元測試，驗證 Java List Sort Example 是否符合預期。

package org.ruoxue.java_147.list.sort;

import static org.assertj.core.api.Assertions.assertThat;

import java.util.Comparator;
import java.util.List;

import org.junit.Test;

import com.google.common.collect.Lists;

public class ListSortWithExamplesTest {

	@Test
	public void sort() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d);
		System.out.println(list);

		list.sort(null);
		System.out.println(list);
		assertThat(list).containsExactly(-1d, 3d, Double.MAX_VALUE);
	}

	@Test
	public void sortWithReverseOrder() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d);
		System.out.println(list);

		list.sort(Comparator.reverseOrder());
		System.out.println(list);
		assertThat(list).containsExactly(Double.MAX_VALUE, 3d, -1d);
	}

	@Test
	public void sortWithComparator() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d);
		System.out.println(list);

		list.sort((i1, i2) -> Double.compare(i1, i2));
		System.out.println(list);
		assertThat(list).containsExactly(-1d, 3d, Double.MAX_VALUE);
	}

	@Test
	public void sortWithComparing() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d);
		System.out.println(list);

		list.sort(Comparator.comparing(Double::doubleValue));
		System.out.println(list);
		assertThat(list).containsExactly(-1d, 3d, Double.MAX_VALUE);
	}

	@Test
	public void sortWithComparingDouble() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d);
		System.out.println(list);

		list.sort(Comparator.comparingDouble(d -> d));
		System.out.println(list);
		assertThat(list).containsExactly(-1d, 3d, Double.MAX_VALUE);
	}

	protected static Comparator<Double> valueComparator = new Comparator<Double>() {
		@Override
		public int compare(Double i1, Double i2) {
			return Double.compare(i1, i2);
		}
	};

	protected static Comparator<Double> lengthComparator = (i1, i2) -> Double.compare(String.valueOf(i1).length(),
			String.valueOf(i2).length());

	@Test
	public void sortWithMultipleConditions() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d);
		System.out.println(list);

		list.sort(valueComparator.thenComparing(lengthComparator));
		System.out.println(list);
		assertThat(list).containsExactly(-1d, 3d, Double.MAX_VALUE);
	}

	@Test
	public void sortWithNull() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d, null);
		System.out.println(list);

		list.sort((s1, s2) -> {
			if (s1 == null) {
				return s2 == null ? 0 : -1;
			} else if (s2 == null) {
				return 1;
			}
			return s1.compareTo(s2);
		});
		System.out.println(list);
		assertThat(list).containsExactly(null, -1d, 3d, Double.MAX_VALUE);
	}

	@Test
	public void sortWithNullsFirst() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d, null);
		System.out.println(list);

		list.sort(Comparator.nullsFirst(Comparator.comparing(s -> s)));
		System.out.println(list);
		assertThat(list).containsExactly(null, -1d, 3d, Double.MAX_VALUE);
	}

	@Test
	public void sortWithNullsLast() {
		List<Double> list = Lists.newArrayList(Double.MAX_VALUE, -1d, 3d, null);
		System.out.println(list);

		list.sort(Comparator.nullsLast(Comparator.comparing(s -> s)));
		System.out.println(list);
		assertThat(list).containsExactly(-1d, 3d, Double.MAX_VALUE, null);
	}
}

心得分享

Java List Sort Example 提供了幾種 Sort 常見方法的操作範例，對不同類型的資料進行排序，像是字串、數字和物件，對資料進行排序可能很有用，例如：文章可以根據用戶設定的要求，像是：修改日期、評論、熱門文章，以多種方式排序，熟悉 List Sort Java 這些方法的操作，讓排序依照不同的需求，快速方便地實現功能。

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