Set<String> set = new TreeSet<>(new Comparator<String>()
时间: 2024-06-05 19:09:17 浏览: 18
这是一个使用自定义比较器的TreeSet集合的初始化语句。TreeSet是一个有序的集合,它会自动将元素按照默认的比较规则(自然排序)进行排序。但是,如果我们想要按照自定义的比较规则进行排序,就需要提供一个实现了Comparator接口的自定义比较器。
在这个例子中,我们创建了一个TreeSet集合,其中元素的类型为String,比较器为一个匿名内部类,该内部类实现了Comparator接口,并重写了其中的compare方法,用于定义字符串的比较规则。由于我们没有提供具体的比较规则,所以这个比较器是无意义的,只是作为示例。
相关问题
import java.util.*; public class Main { public static void main(String[] args) { TreeMap<String, Student> map = new TreeMap<String, Student>(new MyComparator()); Scanner sc = new Scanner(System.in); while (true) { String ID = sc.next(); if (ID.equals("end")) { break; } String name = sc.next(); int score = sc.nextInt(); Student student = new Student(ID, name, score); map.put(ID, student); } Set<String> keyset = new TreeSet<>(); keyset = map.keySet(); for (String key : keyset) { Student student = map.get(key); System.out.println(student.getID() + " " + student.getName() + " " + student.getScore()); } } } class Student { private String ID;//学号 private String name;//姓名 private int score;//成绩 public Student() { } public Student(String ID, String name, int score) { this.ID = ID; this.name = name; this.score = score; } public String getID() { return ID; } public void setID(String ID) { this.ID = ID; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getScore() { return score; } public void setScore(int score) { this.score = score; } } class MyComparator implements Comparator<String> { TreeMap<String, Student> map = new TreeMap<String, Student>(); public MyComparator() { } public MyComparator(TreeMap<String, Student> map) { this.map = map; } @Override public int compare(String o1, String o2) { Student s1 = map.get(o1); Student s2 = map.get(o2); if (s1.getScore() < s2.getScore()) { return 1; } else if (s1.getScore() > s2.getScore()) { return -1; } else { return 0; } } }我想要把根据成绩排序改为根据学号从大到小排序
要按照学号从大到小排序,你可以将 `TreeMap` 的泛型参数中 `String` 改为 `Integer`,这样可以将学号转换为整数类型进行比较。同时,你也需要修改 `MyComparator` 中的 `compare` 方法,将比较逻辑改为根据学号从大到小排序,例如:
```java
class MyComparator implements Comparator<Integer> {
TreeMap<Integer, Student> map;
public MyComparator(TreeMap<Integer, Student> map) {
this.map = map;
}
@Override
public int compare(Integer o1, Integer o2) {
Student s1 = map.get(o1);
Student s2 = map.get(o2);
return o2.compareTo(o1);
}
}
```
在 `compare` 方法中,我们首先获取到要比较的两个学生对象 `s1` 和 `s2`,然后通过比较它们的学号大小来决定它们的顺序。由于要按照学号从大到小排序,因此我们将 `o2` 和 `o1` 进行比较,这样就可以实现根据学号从大到小排序的功能了。
import java.util.*; public class Main { public static void main(String[] args) { TreeMap<String, Student> map = new TreeMap<String,Student>(); Scanner sc = new Scanner(System.in); while(true){ String ID = sc.next(); if(ID.equals("end")){ break; } String name = sc.next(); int score = sc.nextInt(); Student student = new Student(ID,name,score); map.put(ID,student); } Set<String> keyset = new TreeSet<>(); keyset = map.keySet(); for(String key:keyset){ Student student = map.get(key); System.out.println(student.getID() + " " + student.getName() + " " + student.getScore()); } } } class Student{ private String ID;//学号 private String name;//姓名 private int score;//成绩 public Student() { } public Student(String ID, String name, int score) { this.ID = ID; this.name = name; this.score = score; } public String getID() { return ID; } public void setID(String ID) { this.ID = ID; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getScore() { return score; } public void setScore(int score) { this.score = score; } }我这样的代码要改成由从小到大变为由大到小排列,应该怎么处理
可以通过实现 Comparator 接口,并重写 compare 方法来实现 TreeMap 的排序方式的改变。具体的做法是,定义一个新的类 MyComparator 实现 Comparator 接口,在 compare 方法中将两个 Student 对象的成绩 score 进行比较,选择大的那个进行排序。然后在 TreeMap 的构造函数中传入 MyComparator 对象即可。
下面是修改后的代码:
```java
import java.util.*;
public class Main {
public static void main(String[] args) {
TreeMap<String, Student> map = new TreeMap<String, Student>(new MyComparator());
Scanner sc = new Scanner(System.in);
while (true) {
String ID = sc.next();
if (ID.equals("end")) {
break;
}
String name = sc.next();
int score = sc.nextInt();
Student student = new Student(ID, name, score);
map.put(ID, student);
}
Set<String> keyset = new TreeSet<>();
keyset = map.keySet();
for (String key : keyset) {
Student student = map.get(key);
System.out.println(student.getID() + " " + student.getName() + " " + student.getScore());
}
}
}
class Student {
private String ID;//学号
private String name;//姓名
private int score;//成绩
public Student() {
}
public Student(String ID, String name, int score) {
this.ID = ID;
this.name = name;
this.score = score;
}
public String getID() {
return ID;
}
public void setID(String ID) {
this.ID = ID;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getScore() {
return score;
}
public void setScore(int score) {
this.score = score;
}
}
class MyComparator implements Comparator<String> {
TreeMap<String, Student> map = new TreeMap<String, Student>();
public MyComparator() {
}
public MyComparator(TreeMap<String, Student> map) {
this.map = map;
}
@Override
public int compare(String o1, String o2) {
Student s1 = map.get(o1);
Student s2 = map.get(o2);
if (s1.getScore() < s2.getScore()) {
return 1;
} else if (s1.getScore() > s2.getScore()) {
return -1;
} else {
return 0;
}
}
}
```
在 MyComparator 类中,我们将 TreeMap 对象作为成员变量传入,这样在 compare 方法中就可以通过 map.get() 方法获取到相应的 Student 对象,进而进行比较。通过此方法,就可以实现由大到小的排序方式。
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