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Java Arrays sort Method - Java 147

Java Arrays sort Method – Java 147

Java Arrays sort Method

在 Java 中對資料進行排序，提供 Arrays sort 方法操作排序，預設會按升序對集合進行排序，當資料需要按特定順序排列，可以實作 Comparator 接口，使用傳統方式或 Lambda 表達式來實作其功能， Sort Java Arrays 提供了預設比較器和建立自定義比較器，對資料進行排序，本篇增加了範例，並透過單元測試來驗證產出結果。

public static void sort(Object[] a) {
}

public static <T> void sort(T[] a, Comparator<? super T> c) {
}

檔案目錄

./
   +- src
       +- test
       |   +- org
       |       +- ruoxue
       |           +- java_147
       |               +- array
       |                   +- sort
       |                       +- ArraysSortTest.java

單元測試

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

sort

Arrays Sort Java 建立一個 Array ，增加三個元素，使用 Arrays 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() {
		String[] array = new String[] { "Guava", "Durian", "Pitaya" };
		System.out.println(Arrays.toString(array));

		Arrays.sort(array);
		System.out.println(Arrays.toString(array));
		assertThat(array).containsExactly("Durian", "Guava", "Pitaya");
	}
[Guava, Durian, Pitaya]
[Durian, Guava, Pitaya]

sortWithReverseOrder

Arrays Sort Java 建立一個 Array ，增加三個元素，使用 Arrays sort 方法，依照預設反向比較器，由大到小，降序對集合進行排序。

	@Test
	public void sortWithReverseOrder() {
		String[] array = new String[] { "Guava", "Durian", "Pitaya" };
		System.out.println(Arrays.toString(array));

		Arrays.sort(array, Comparator.reverseOrder());
		System.out.println(Arrays.toString(array));
		assertThat(array).containsExactly("Pitaya", "Guava", "Durian");
	}
[Guava, Durian, Pitaya]
[Pitaya, Guava, Durian]

sortWithComparator

Arrays Sort Java 建立一個 Array ，增加三個元素，使用 Arrays 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() {
		String[] array = new String[] { "Guava", "Durian", "Pitaya" };
		System.out.println(Arrays.toString(array));

		Arrays.sort(array, (s1, s2) -> s1.length() - s2.length());
		System.out.println(Arrays.toString(array));
		assertThat(array).containsExactly("Guava", "Durian", "Pitaya");
	}
[Guava, Durian, Pitaya]
[Guava, Durian, Pitaya]

sortWithComparing

Arrays Sort Example 建立一個 Array ，增加三個元素，使用 Arrays 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() {
		String[] array = new String[] { "Guava", "Durian", "Pitaya" };
		System.out.println(Arrays.toString(array));

		Arrays.sort(array, Comparator.comparing(String::length));
		System.out.println(Arrays.toString(array));
		assertThat(array).containsExactly("Guava", "Durian", "Pitaya");
	}
[Guava, Durian, Pitaya]
[Guava, Durian, Pitaya]

sortWithMultipleConditions

Arrays Sort Example 建立一個 Array ，增加三個元素，使用 Arrays 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<String> nameComparator = new Comparator<String>() {
		@Override
		public int compare(String s1, String s2) {
			return s1.compareTo(s2);
		}
	};

	protected static Comparator<String> lengthComparator = (s1, s2) -> Integer.compare(s1.length(), s2.length());

	@Test
	public void sortWithMultipleConditions() {
		String[] array = new String[] { "Guava", "Durian", "Pitaya" };
		System.out.println(Arrays.toString(array));

		Arrays.sort(array, nameComparator.thenComparing(lengthComparator));
		System.out.println(Arrays.toString(array));
		assertThat(array).containsExactly("Durian", "Guava", "Pitaya");
	}
[Guava, Durian, Pitaya]
[Durian, Guava, Pitaya]

sortWithNull

建立一個 Array ，增加三個元素及一個 null 元素，使用 Arrays 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() {
		String[] array = new String[] { "Guava", "Durian", "Pitaya", null };
		System.out.println(Arrays.toString(array));

		Arrays.sort(array, (s1, s2) -> {
			if (s1 == null) {
				return s2 == null ? 0 : -1;
			} else if (s2 == null) {
				return 1;
			}
			return s1.compareTo(s2);
		});
		System.out.println(Arrays.toString(array));
		assertThat(array).containsExactly(null, "Durian", "Guava", "Pitaya");
	}
[Guava, Durian, Pitaya, null]
[null, Durian, Guava, Pitaya]

sortWithNullsFirst

建立一個 Array ，增加三個元素及一個 null 元素，使用 Arrays 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() {
		String[] array = new String[] { "Guava", "Durian", "Pitaya", null };
		System.out.println(Arrays.toString(array));

		Arrays.sort(array, Comparator.nullsFirst(Comparator.comparing(s -> s)));
		System.out.println(Arrays.toString(array));
		assertThat(array).containsExactly(null, "Durian", "Guava", "Pitaya");
	}
[Guava, Durian, Pitaya, null]
[null, Durian, Guava, Pitaya]

sortWithNullsLast

建立一個 Array ，增加三個元素及一個 null 元素，使用 Arrays 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() {
		String[] array = new String[] { "Guava", "Durian", "Pitaya", null };
		System.out.println(Arrays.toString(array));

		Arrays.sort(array, Comparator.nullsLast(Comparator.comparing(s -> s)));
		System.out.println(Arrays.toString(array));
		assertThat(array).containsExactly("Durian", "Guava", "Pitaya", null);
	}
[Guava, Durian, Pitaya, null]
[Durian, Guava, Pitaya, null]

ArraysSortTest.java

Arrays Sort Example 新增單元測試，驗證是否符合預期。

package org.ruoxue.java_147.array.sort;

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

import java.util.Arrays;
import java.util.Comparator;

import org.junit.Test;

public class ArraysSortTest {

	@Test
	public void sort() {
		String[] array = new String[] { "Guava", "Durian", "Pitaya" };
		System.out.println(Arrays.toString(array));

		Arrays.sort(array);
		System.out.println(Arrays.toString(array));
		assertThat(array).containsExactly("Durian", "Guava", "Pitaya");
	}

	@Test
	public void sortWithReverseOrder() {
		String[] array = new String[] { "Guava", "Durian", "Pitaya" };
		System.out.println(Arrays.toString(array));

		Arrays.sort(array, Comparator.reverseOrder());
		System.out.println(Arrays.toString(array));
		assertThat(array).containsExactly("Pitaya", "Guava", "Durian");
	}

	@Test
	public void sortWithComparator() {
		String[] array = new String[] { "Guava", "Durian", "Pitaya" };
		System.out.println(Arrays.toString(array));

		Arrays.sort(array, (s1, s2) -> s1.length() - s2.length());
		System.out.println(Arrays.toString(array));
		assertThat(array).containsExactly("Guava", "Durian", "Pitaya");
	}

	@Test
	public void sortWithComparing() {
		String[] array = new String[] { "Guava", "Durian", "Pitaya" };
		System.out.println(Arrays.toString(array));

		Arrays.sort(array, Comparator.comparing(String::length));
		System.out.println(Arrays.toString(array));
		assertThat(array).containsExactly("Guava", "Durian", "Pitaya");
	}

	protected static Comparator<String> nameComparator = new Comparator<String>() {
		@Override
		public int compare(String s1, String s2) {
			return s1.compareTo(s2);
		}
	};

	protected static Comparator<String> lengthComparator = (s1, s2) -> Integer.compare(s1.length(), s2.length());

	@Test
	public void sortWithMultipleConditions() {
		String[] array = new String[] { "Guava", "Durian", "Pitaya" };
		System.out.println(Arrays.toString(array));

		Arrays.sort(array, nameComparator.thenComparing(lengthComparator));
		System.out.println(Arrays.toString(array));
		assertThat(array).containsExactly("Durian", "Guava", "Pitaya");
	}

	@Test
	public void sortWithNull() {
		String[] array = new String[] { "Guava", "Durian", "Pitaya", null };
		System.out.println(Arrays.toString(array));

		Arrays.sort(array, (s1, s2) -> {
			if (s1 == null) {
				return s2 == null ? 0 : -1;
			} else if (s2 == null) {
				return 1;
			}
			return s1.compareTo(s2);
		});
		System.out.println(Arrays.toString(array));
		assertThat(array).containsExactly(null, "Durian", "Guava", "Pitaya");
	}

	@Test
	public void sortWithNullsFirst() {
		String[] array = new String[] { "Guava", "Durian", "Pitaya", null };
		System.out.println(Arrays.toString(array));

		Arrays.sort(array, Comparator.nullsFirst(Comparator.comparing(s -> s)));
		System.out.println(Arrays.toString(array));
		assertThat(array).containsExactly(null, "Durian", "Guava", "Pitaya");
	}

	@Test
	public void sortWithNullsLast() {
		String[] array = new String[] { "Guava", "Durian", "Pitaya", null };
		System.out.println(Arrays.toString(array));

		Arrays.sort(array, Comparator.nullsLast(Comparator.comparing(s -> s)));
		System.out.println(Arrays.toString(array));
		assertThat(array).containsExactly("Durian", "Guava", "Pitaya", null);
	}
}

心得分享

Java Arrays Sort 排序是指使用特定標準以特定順序排列資料，可以對不同類型的資料進行排序，像是字串、數字和物件，提供了幾種 Sort 常見方法的操作範例，在應用上相當廣泛，熟悉 Arrays Sort Example 這些方法的操作，可以讓排序依照不同的需求，更簡易、快速地實現功能。

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