Stream流常見的中間方法

Stream流常見的終結方法

代碼

學生類（代碼一與代碼二共涉及到的類）

package com.itheima.day28_Stream;import java.util.Objects;public class Student implements Comparable<Student> {private String name;private int age;private double height;@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", age=" + age +", height=" + height +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;Student student = (Student) o;return age == student.age && Double.compare(height, student.height) == 0 && Objects.equals(name, student.name);}@Overridepublic int hashCode() {return Objects.hash(name, age, height);}public Student() {}public Student(String name, int age, double height) {this.name = name;this.age = age;this.height = height;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public double getHeight() {return height;}public void setHeight(double height) {this.height = height;}@Overridepublic int compareTo(Student o) {return this.age - o.age;//年齡升序排序}
}

代碼一：掌握Stream流提供的常見中間方法

package com.itheima.day28_Stream;import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.stream.Stream;//目標:掌握Stream流提供的常見中間方法
public class StreamTest3 {public static void main(String[] args) {List<Double> scores = new ArrayList<>();Collections.addAll(scores,88.5,56.6,58.8,89.9,100.0,16.6);// 需求1:找出成績大于等于60分的數據，并升序后，再輸出。scores.stream().filter(s->s>=60).sorted().forEach(s->System.out.println(s));List<Student>students =new ArrayList<>();Student s1 = new Student("蜘蛛精",26,172.5);Student s2 = new Student("蜘蛛精",26, 172.5);Student s3 = new Student( "紫霞",23, 167.6);Student s4 = new Student("白晶品", 25,169.0);Student s5 = new Student("牛魔王",35,183.3);Student s6 =new Student( "牛夫人", 34,168.5);Collections.addAll(students,s1,s2,s3,s4,s5,s6);// 需求2:找出年齡大于等于23,且年齡小于等于30歲的學生，并按照年齡降序輸出.students.stream().filter(s -> s.getAge()>=23 && s.getAge()<=30).sorted((o1,o2)-> o2.getAge()-o1.getAge())//使用lambda簡寫，年齡降序排列.forEach(s->System.out.println(s));System.out.println("===========================================");//需求3:取出身高最高的前3名學生，并輸出。students.stream().sorted((o1,o2)->Double.compare(o2.getHeight(),o1.getHeight())).limit(3).forEach(System.out::println);System.out.println("===========================================");// 需求4:取出身高倒數的2名學生，并輸出。students.stream().sorted((o1,o2)->Double.compare(o2.getHeight(),o1.getHeight())).skip(students.size()-2).forEach(System.out::println);System.out.println("===========================================");// 需求5:找出身高超過168的學生叫什么名字，要求去除重復的名字，再輸出。students.stream().filter(s->s.getHeight()>168).map(Student::getName)//把原來的學生對象集合加工（映射）成為名字集合.distinct()//去除重復的名字.forEach(System.out::println);System.out.println("===========================================");// distinct去重復，自定義類型的對象(希望內容一樣就認為重復，重寫hashCode,equals)students.stream().distinct().forEach(System.out::println);System.out.println("===========================================");//合并兩個stream流Stream<String> str1 = Stream.of("張三", "李四");Stream<String> str2 = Stream.of("張3", "李4","王五");Stream<String> Allst = Stream.concat(str1, str2);Allst.forEach(System.out::println);}
}

代碼二：掌握Stream流提供的常見終結方法

package com.itheima.day28_Stream;import java.util.*;
import java.util.stream.Collectors;
//目標:掌握Stream流提供的常見終結方法
public class StreamTest4 {public static void main(String[] args) {List<Student> students =new ArrayList<>();Student s1 = new Student("蜘蛛精",26,172.5);Student s2 = new Student("蜘蛛精",26, 172.5);Student s3 = new Student( "紫霞",23, 167.6);Student s4 = new Student("白晶品", 25,169.0);Student s5 = new Student("牛魔王",35,183.3);Student s6 =new Student( "牛夫人", 34,168.5);Collections.addAll(students,s1,s2,s3,s4,s5,s6);// 需求1:請計算出身高超過168的學生有幾人。long count = students.stream().filter(s -> s.getHeight() > 168).count();System.out.println(count);System.out.println("===================================");// 需求2:請找出身高最高的學生對象，并輸出。Student stu1 = students.stream().max((o1, o2) -> Double.compare(o1.getHeight(), o2.getHeight())).get();System.out.println(stu1);System.out.println("===================================");// 需求3:請找出身高最矮的學生對象，并輸出。Student stu2 = students.stream().min((o1, o2) -> Double.compare(o1.getHeight(), o2.getHeight())).get();System.out.println(stu2);System.out.println("===================================");// 需求4:請找出身高超過170的學生對象，并放到一個新集合中去返回。//流只能收集一次,因此"students.stream().filter(s -> s.getHeight() > 170)"不能單獨作為新的stream流分別取做collect(Collectors.toList())與collect(Collectors.toSet())操作List<Student> students1 = students.stream().filter(s -> s.getHeight() > 170).collect(Collectors.toList());System.out.println(students1);Set<Student> students2 = students.stream().filter(s -> s.getHeight() > 170).collect(Collectors.toSet());System.out.println(students2);// 需求5:請找出身高超過170的學生對象，并把學生對象的名字和身高，存入到一個Map集合返回。System.out.println("===================================");Map<String, Double> map = students.stream().filter(s -> s.getHeight() > 170).distinct()//map集合的元素不可重復，因此先去重.collect(Collectors.toMap(a -> a.getName(), a -> a.getHeight()));System.out.println(map);System.out.println("===================================");//存入到數組//寫法1Object[] array1 = students.stream().filter(s -> s.getHeight() > 170).toArray();System.out.println(Arrays.toString(array1));System.out.println("======================================");//寫法2Student[] array2 = students.stream().filter(s -> s.getHeight() > 170).toArray(len -> new Student[len]);System.out.println(Arrays.toString(array2));}
}