Java集合流_編程題

2020/5/6
主要題目都註釋在主函數及下面的方法中
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Student 類

public class Student {
    private int number;
    private String name;
    private String clazz;
    private int score;
    public Student(int number, String name, String clazz, int score) {
        this.number = number;
        this.name = name;
        this.clazz = clazz;
        this.score = score;
    }
    // 省略getter/setter方法
    public int getScore() {
    	return score;
    }
    public int getNumber() {
    	return number;
    }
    public String getName() {
    	return name;
    }
    public String getClazz() {
    	return clazz;
    }
}

StreamTest.java

import java.util.*;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class StreamTest {
    private static final List <Student> STUDENTS = create();
    private static final String CLAZZ1 = "軟件1班";
    private static final String CLAZZ2 = "軟件2班";
    
    private static List <Student> create() {
        Student s1 = new Student(2018008, "張揚", CLAZZ2, 66);
        Student s2 = new Student(2018005, "劉飛", CLAZZ1, 92);
        Student s3 = new Student(2018007, "李明", CLAZZ2, 42);
        Student s4 = new Student(2018006, "趙勇", CLAZZ2, 56);
        Student s5 = new Student(2018002, "王磊", CLAZZ1, 81);
        Student s6 = new Student(2018010, "牛娜", CLAZZ1, 78);
        List<Student> students = new ArrayList<>();
        students.add(s1);students.add(s2);students.add(s3);
        students.add(s4);students.add(s5);students.add(s6);
        return students;
    }
    
    public static void main(String[] args) {
    	// 調用實現方法測試
    	//f4(STUDENTS);
    	//f5(STUDENTS,95,"軟件1班");
    	// f6(STUDENTS,95,"軟件1班");
    	f7(STUDENTS,95,"軟件1班");   
    }
    
    // 以下都是實現方法————
    public static void f7(List <Student> s,int grade,String b){
    	//獲取指定班級，成績小於等於指定分數，的全部學生
        //以學生學號爲鍵，學生分數爲值，Map分組，返回
        s.stream()
        .filter(a->a.getScore()<=grade&&b.equals(a.getClazz()))
        .collect(Collectors.toMap(a->a.getNumber(),a->a.getScore()))
        .forEach((k,v)->{            
        	System.out.println(k+" "+v);            
        });
    }
    
    public static void f6(List <Student> s,int grade,String b){
    	//獲取指定班級，成績小於等於指定分數，成績由高到低排序，的全部學生的學號
        s.stream()
        .filter(a->a.getScore()<=grade&&b.equals(a.getClazz()))
        .sorted(Comparator.comparing(Student::getScore).reversed())
        .collect(Collectors.toList())
        .forEach(a->{            
        	System.out.println(a.getNumber());           
        }); 
    }
    
    public static void f5(List <Student> s,int grade,String b){
    	// 獲取指定班級，成績小於等於指定分數，成績由高到低排序，的全部學生
        s.stream()            
        .filter(a->a.getScore()<=grade&&b.equals(a.getClazz()))            
        .sorted(Comparator.comparing(Student::getScore).reversed())            
        .collect(Collectors.toList())
        .forEach(a->{            
        	System.out.println(a.getNumber()+" "+a.getName()+" "+a.getClazz()+" "+a.getScore());
        }); 
    }
    
    public static void f4(List <Student> s){
    	//方法4，按成績由低到高排序，返回全部學生
        s.stream()            
        .sorted(Comparator.comparing(a->a.getScore()))            
        .collect(Collectors.toList())            
        .forEach(a->{            
        	System.out.println(a.getNumber()+""+a.getName()+" "+a.getClazz()+" "+a.getScore());            
        	}); 
    }
    
    public static List<Student> f2(List<Student> s,int grade,String b){   
    	return s.stream()   
    			.filter(a->a.getScore()<=grade&&b.equals(a.getClazz()))   
    			.collect(Collectors.toList());   
    }
    
    private static List<Student> fangfa1(){
    	// 獲取70分以下的人
    	List<Student> newlist = new ArrayList<>();
    	for(Student stu : STUDENTS) {
    		if(stu.getScore()<70)
    			newlist.add(stu);
    	}
    	return newlist;
    }
}