stream流的thenComparing使用和reversed理解

Author: 曾梓健

myTest/src/main/java/com/hand/streamSort/Stu.java

@@ -0,0 +1,82 @@
+package com.hand.streamSort;
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+
+/**
+ * @author zijian.zeng@hand-china.com
+ * @since 2023-02-09
+ */
+public class Stu {
+	String name;
+	int age;
+
+	public Stu(String name, int age) {
+		this.name = name;
+		this.age = age;
+	}
+
+	public String getName() {
+		return name;
+	}
+
+	public int getAge() {
+		return age;
+	}
+
+	@Override
+	public String toString() {
+		return "Stu{" +
+				"name='" + name + '\'' +
+				", age=" + age +
+				'}';
+	}
+
+	public static void main(String[] args) {
+		List<Stu> stul = new ArrayList<>();
+		stul.add(new Stu("b", 19));
+		stul.add(new Stu("c", 17));
+		stul.add(new Stu("a", 19));
+		stul.add(new Stu("d", 18));
+		stul.add(new Stu("b", 17));
+		stul.add(new Stu("a", 17));
+		stul.add(new Stu("c", 19));
+		stul.add(new Stu("c", 18));
+
+
+		/**
+		 * 0 : 先把数据按照名称排序，再将排序结果按照年龄排序
+		 * 1 ：先把数据按照名称排序，再在按照名称排序基础上，对相同名称的数据按照年龄排序
+		 *
+		 */
+//		System.out.println("-0-");
+//		stul.stream().sorted(Comparator.comparing(Stu::getName)).sorted(Comparator.comparing(Stu::getAge))
+//				.forEachOrdered(stu -> System.out.println("name:" + stu.getName() + ";age:" + stu.getAge()));
+//		System.out.println("-1-");
+//		stul.stream().sorted(Comparator.comparing(Stu::getName).thenComparing(Stu::getAge))
+//				.forEachOrdered(stu -> System.out.println("name:" + stu.getName() + ";age:" + stu.getAge()));
+
+		System.out.println("-2-");
+		stul.stream().sorted(Comparator.comparing(Stu::getAge).thenComparing(Stu::getName))
+				.forEachOrdered(stu -> System.out.println("name:" + stu.getName() + ";age:" + stu.getAge()));
+
+		System.out.println("-3-");
+		stul.stream().sorted(Comparator.comparing(Stu::getAge).thenComparing(Stu::getName).reversed())
+				.forEachOrdered(stu -> System.out.println("name:" + stu.getName() + ";age:" + stu.getAge()));
+
+		System.out.println("-4-");
+		stul.stream().sorted(Comparator.comparing(Stu::getAge).reversed().thenComparing(Stu::getName))
+				.forEachOrdered(stu -> System.out.println("name:" + stu.getName() + ";age:" + stu.getAge()));
+
+
+		/**
+		 * 这个例子深刻理解：reversed()作用：
+		 * 先age升，然后reversed，得到age降，第二个name升，再reversed（当前age降name升）得到age升name降；
+		 */
+		System.out.println("-5-");
+		stul.stream().sorted(Comparator.comparing(Stu::getAge).reversed().thenComparing(Stu::getName).reversed())
+				.forEachOrdered(stu -> System.out.println("name:" + stu.getName() + ";age:" + stu.getAge()));
+	}
+}
+