对已经在 Java 中实现了可比的数组和包装类的元素进行排序
原文:https://www . geeksforgeeks . org/排序-数组元素和包装类-已经在 java 中实现了可比较的/
Java 提供了可比较的接口，可以使用类的数据成员对对象进行排序。可比界面只包含一个方法 【比较】( )来比较两个对象，以在它们之间强加一个顺序。它返回一个负整数、零或正整数，以指示输入对象是否小于、等于 、 或大于当前对象。它主要用于对自定义对象的数组或列表进行排序。
由于所有的包装类都已经实现了 Java Comparable 接口，所以它提供了 compareTo() 的默认实现，这就是为什么T5】collections . sort()T7】和T9】arrays . sort()函数可以在这些对象上使用的原因。将包含包装类的数组和列表的元素排序为已经实现可比接口的对象。
插图:
Input : {8 , 9 , 1 , 5 , 3 , 0}
Output : {0 , 1 , 3 , 5 , 8 , 9}
Input : {"Ankit", "Parul" , "Swati" , "Tarun", "Akshat"}
Output : {"Akshat" , "Ankit" , "Parul" , "Swati" , "Tarun"}
实施:
示例
Java
// Java Program to Sorting Elements illustrating
// Array.srt) and Collection.sort() method
// Naive approach
// Importing all classes of
// java.util package
import java.util.*;
// Class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Case 1: Array of Integer using sort()
// Sorting array of integers
// using Arrays.sort()
// Custom input entries
int[] a = { 8, 9, 1, 5, 3, 0 };
// Print the array before sorting
System.out.println("Before Sorting: "
+ Arrays.toString(a));
// By default sorting is in ascending order
Arrays.sort(a);
// Print the array after sorting
System.out.println("After Sorting: "
+ Arrays.toString(a));
// Case 2: Array of string using sort()
// Sorting array of Strings
// using Arrays.sort()
String[] str = { "Ankit", "Parul", "Swati", "Tarun",
"Akshat" };
// Print the input array of string before sorting
System.out.println("Before Sorting: "
+ Arrays.toString(str));
// Sort() method
Arrays.sort(str);
// Print the input array of string before sorting
System.out.println("After Sorting: "
+ Arrays.toString(str));
// Case 3: Collectios.sort
// Sorting List of String Collections.sort()
// Creating an list object of string type
// Custominput elements in object
List<String> lt = Arrays.asList("Red", "Blue",
"Green", "Black");
// Print the elements before sorting
System.out.println("Before Sorting: " + lt);
Collections.sort(lt);
// Print the elements after sorting
System.out.println("After Sorting:: " + lt);
}
}
输出
Before Sorting: [8, 9, 1, 5, 3, 0]
After Sorting: [0, 1, 3, 5, 8, 9]
Before Sorting: [Ankit, Parul, Swati, Tarun, Akshat]
After Sorting: [Akshat, Ankit, Parul, Swati, Tarun]
Before Sorting: [Red, Blue, Green, Black]
After Sorting:: [Black, Blue, Green, Red]
现在，如果我们想将一个用户定义的类排序成某种特定的顺序，那么我们必须实现存在于 java.lang 包中的 Comparable 接口，并提供comparto()方法的实现。如果指定的为空或者如果指定对象的类型阻止它与对象进行比较，compareTo 方法还会抛出一个空指针异常或 ClassCastException 。
实施:
示例
Java
// Java Program to Sorting Elements of Arrays and Wrapper
// Classes that Already Implements Comparable
// Importing all classes from
// java.util package
import java.util.*;
// Class 1
// Helper class
class Student implements Comparable<Student> {
// Member variables of this class
private int rollno;
private String name;
private Double marks;
// Constructor of this class
public Student(int rollno, String name, Double marks)
{
// This keyword refers to
// current object itself
this.rollno = rollno;
this.name = name;
this.marks = marks;
}
// Sorting based on marks of Students
public int compareTo(Student s)
{
return this.marks.compareTo(s.marks);
}
public String toString()
{
return "Student{"
+ "RollNo=" + rollno + ", Name='" + name + '\''
+ ", Marks=" + marks + '}';
}
}
// Class 2
// Main class
class GFG {
// main driver method
public static void main(String args[])
{
// Creating an ArrayList of user-defined
// type(Student)
ArrayList<Student> arr = new ArrayList<>();
// Adding elements to object created above
// Custom input entries
arr.add(new Student(1, "Ankush", 98.0));
arr.add(new Student(2, "Akshat", 99.0));
arr.add(new Student(3, "Parul", 87.0));
arr.add(new Student(4, "Tarun", 78.0));
arr.add(new Student(5, "Swati", 90.0));
// Iterating over the above ArrayList
for (int i = 0; i < arr.size(); i++)
// Print the ArrayList elements as
// in order added
System.out.println(arr.get(i));
// Calling the Collection.sort() method
// to sort elements od ArrayList
Collections.sort(arr);
// Printing the ArrayList after sorting
System.out.println("\nAfter Sorting :\n");
for (int i = 0; i < arr.size(); i++)
System.out.println(arr.get(i));
}
}
输出
Student{RollNo=1, Name='Ankush', Marks=98.0}
Student{RollNo=2, Name='Akshat', Marks=99.0}
Student{RollNo=3, Name='Parul', Marks=87.0}
Student{RollNo=4, Name='Tarun', Marks=78.0}
Student{RollNo=5, Name='Swati', Marks=90.0}
After Sorting :
Student{RollNo=4, Name='Tarun', Marks=78.0}
Student{RollNo=3, Name='Parul', Marks=87.0}
Student{RollNo=5, Name='Swati', Marks=90.0}
Student{RollNo=1, Name='Ankush', Marks=98.0}
Student{RollNo=2, Name='Akshat', Marks=99.0}
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