比較器排序

• 比較器排序：
  採用有參構造，構造的引數就要一個比較器

 TreeSet(Comparator<? super E> comparator)

• 在建立TreeSet 物件的時候，傳進來一個比較器的子類物件
  根據子類物件重寫比較器中compare 方法，根據此方法的返回值的正負和0，來排序元素，返回0就不往裡面存
  a.構造一個新的空 TreeSet，它根據指定比較器進行排序。
  b.介面 Comparator 比較器
  c.int compare(T o1, T o2) 比較方法
  d.比較用來排序的兩個引數。

public
 
 class MyTest3 {

        public static void main(String[] args) {

        TreeSet t = new TreeSet<>(new Comparator<Integer>() {
            @Override
            public int compare(Integer s1, Integer s2) {
                return s1 - s2;
            }
        });
        t.add(6);
        t.add(6
 
);
        t.add(3);
        t.add(2);
        t.add(1);
        t.add(4);
        t.add(5);
        t.add(4);
        t.add(3);
        System.out.println(t);
        //[1, 2, 3, 4, 5, 6]
    }
}

• 舉例：鍵盤錄入3個學生資訊(姓名,語文成績,數學成績,英語成績),按照總分從高到低輸出到控制檯。

//Student類
public class Student {
    private String name;
    private
 
 double mathScore;
    private double englishScore;
    private double totalScote;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getMathScore() {
        return mathScore;
    }

    public void setMathScore(double mathScore) {
        this.mathScore = mathScore;
    }

    public double getEnglishScore() {
        return englishScore;
    }

    public void setEnglishScore(double englishScore) {
        this.englishScore = englishScore;
    }


    public double getTotalScote() {
        return this.englishScore+this.mathScore;
    }
}

//測試類
public class MyTest2 {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        //比較器排序
        TreeSet<Student> treeSet = new TreeSet<Student>(new Comparator<Student>() {
            @Override
            public int compare(Student s1, Student s2) {
                return (int) (s1.getTotalScote() - s2.getTotalScote());
            }
        });
        for (int i = 1; i <= 3; i++) {
            System.out.println("請輸入學生的姓名");
            Student student = new Student();
            String name = sc.next();
            student.setName(name);
            System.out.println("請輸入第" + i + "個學生" + name + "的數學成績");
            double mathScore = sc.nextDouble();
            student.setMathScore(mathScore);
            System.out.println("請輸入第" + i + "個學生" + name + "的英語成績");
            double englishScore = sc.nextDouble();
            student.setEnglishScore(englishScore);
            //把學生物件新增到集合裡面
            treeSet.add(student);
        }

        System.out.println("姓名" + "\t" + "數學成績" + "\t" + "總分");
        for (Student stu : treeSet) {
            System.out.println(stu.getName() + "\t" + stu.getMathScore() + "\t" + stu.getEnglishScore() + "\t" + stu.getTotalScote());
        }


    }
}