使用带有用户定义对象的比较器对树形图中的关键字进行排序的 Java 程序
原文:https://www . geesforgeks . org/Java-通过使用带有用户定义对象的比较器对树图中的键进行排序的程序/
Java 中的树形图与抽象图类一起用于实现地图界面和导航地图。地图根据其键的自然顺序进行排序，或者通过地图创建时提供的【比较器】 进行排序，具体取决于使用的构造函数。为了通过在 Java 中使用带有用户定义对象的比较器来对 TreeMap 中的键进行排序，我们必须创建一个实现比较器接口的类来覆盖比较方法。
// AccordingMarks class that implements the
// comparator interface to override compare method
class AccordingMarks implements Comparator<Student> {
public int compare(Student s1, Student s2) {
return s1.getMarks().compareTo(s2.getMarks());
}
}
在下面的代码中，我们将一个自定义对象作为键传递给 TreeMap，即学生用户定义的类。在这种情况下，我们需要在构造器中传递比较器 AccordingMarks ，同时创建根据学生的标记对树形图进行排序的树形图对象。
示例 1: 按标记的升序排列键
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to demonstrate how to sort TreeMap of custom
// class objects
import java.util.*;
// Custom class
class Student {
private String name;
private int marks;
public Student(String name, Integer marks)
{
this.name = name;
this.marks = marks;
}
public String getName() { return this.name; }
public Integer getMarks() { return this.marks; }
// override toString method
public String toString()
{
return this.name + ": " + marks;
}
}
// Comparator that sort elements according to marks in
// Ascending order
class AccordingMarks implements Comparator<Student> {
public int compare(Student s1, Student s2)
{
return s1.getMarks().compareTo(s2.getMarks());
}
}
// Driver Code
public class GFG {
public static void main(String[] args)
{
// New TreeMap of custom class Student
TreeMap<Student, Integer> map
= new TreeMap<>(new AccordingMarks());
// Add elements to TreeMap
map.put(new Student("Akshay", 400), 1);
map.put(new Student("Bina", 500), 2);
map.put(new Student("Chintu", 300), 3);
System.out.println(
"TreeMap keys sorting in ascending order of the marks:");
// Print map using Entry
for (Map.Entry<Student, Integer> entry :
map.entrySet()) {
System.out.println("Key : (" + entry.getKey()
+ "), Value : "
+ entry.getValue());
}
}
}
输出:
TreeMap keys sorting in ascending order of the marks:
Key : (Chintu: 300), Value : 3
Key : (Akshay: 400), Value : 1
Key : (Bina: 500), Value : 2
示例 2: 将键按标记的降序排序
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to demonstrate how to sort TreeMap of custom
// class objects
import java.util.*;
// Custom class
class Student {
private String name;
private int marks;
public Student(String name, Integer marks)
{
this.name = name;
this.marks = marks;
}
public String getName() { return this.name; }
public Integer getMarks() { return this.marks; }
// override toString method
public String toString()
{
return this.name + ": " + marks;
}
}
// Comparator that sort elements according to marks in
// Descending order
class AccordingMarks implements Comparator<Student> {
public int compare(Student s1, Student s2)
{
return s2.getMarks().compareTo(s1.getMarks());
}
}
// Driver Code
public class GFG {
public static void main(String[] args)
{
// New TreeMap of custom class Student
TreeMap<Student, Integer> map
= new TreeMap<>(new AccordingMarks());
// Add elements to TreeMap
map.put(new Student("Akshay", 400), 1);
map.put(new Student("Bina", 500), 2);
map.put(new Student("Chintu", 300), 3);
System.out.println(
"TreeMap Keys sorted in descending order of the marks: ");
// Print map using Entry
for (Map.Entry<Student, Integer> entry :
map.entrySet()) {
System.out.println("Key : (" + entry.getKey()
+ "), Value : "
+ entry.getValue());
}
}
}
输出:
TreeMap Keys sorted in descending order of the marks:
Key : (Bina: 500), Value : 2
Key : (Akshay: 400), Value : 1
Key : (Chintu: 300), Value : 3
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