개체 배열 정렬? 사용자 입력과 비교

Question

Trying to sort an array of objects by overallVisits from greatest to smallest but get an error. The goal is to pass in website objects to the array then have them sorted out according to greatest overall visit to least visit. I get the following error: Exception in thread "main" java.lang.NullPointerException at java.util.ComparableTimSort.binarySort(ComparableTimSort.java:258) at java.util.ComparableTimSort.sort(ComparableTimSort.java:185) at java.util.Arrays.sort(Arrays.java:1246) at Project1.main(Project1.java:32)

import java.util.Scanner; 
import java.util.Arrays; 

public class Project1 
{ 
public static void main (String args[]) 
{ 
Scanner input = new Scanner(System.in); 

Website [] websites = new Website[20]; 

String temp; 
String temp2; 
int days = 4;  

for(int i=0; i < 10; i++) 
{ 
     System.out.println("Enter the URL of the Website:"); 
     temp = input.nextLine(); 
     websites[i] = new Website(); 
     websites[i].setUrl(temp); 

     System.out.println("Enter the name of the Website:"); 
     temp2 = input.nextLine(); 
     websites[i].setName(temp2); 

    } 

Arrays.sort(websites); 

for(int i = 0; i<10; i++) 
{ 
     System.out.println("URL:" + websites[i].getUrl()+ " Current Visits:" +  websites[i].getCurvisit() + " Overall Visits:" + websites[i].getOvrvisit()); 

     System.out.println("Name of Website:" + websites[i].getName()); 

} 

} 
} 
//Class 2: 
import java.util.Scanner; 
import java.util.Random; 

public class Website implements Comparable <Website> 
{ 
private String url; 
private String name; 
private int currentVisit; 
private int overallVisit; 

public Website() 
{ 
    this.url = url; 
    this.name = name; 
    this.currentVisit = getRandom1(); 
    this.overallVisit = getRandom2(); 

} 

public String getUrl() 
{ 
    return url; 
} 

public void setUrl(String s) 
{ 
    url = s; 
} 

public String getName() 
{ 
    return name; 
} 

public void setName(String n) 
{ 
    name = n; 
} 

public int getRandom1() 
{ 
Random rand = new Random(); 

int num = rand.nextInt(4); 
return num; 
} 

public int getRandom2() 
{ 
Random rand = new Random(); 

int num2 = 10 + rand.nextInt(11); 
return num2; 
} 

public int getCurvisit() 
{ 
return currentVisit; 
} 

public int getOvrvisit() 
{ 
    return overallVisit; 
} 

public int compareTo(Website compareVisit) 
{ 
    int compareAll = ((Website) compareVisit).getOvrvisit(); 
    return compareAll - this.overallVisit; 
} 
} 

Answer 1

당신이 당신의 배열의 20 개 요소를 할당했지만에만 필링 (10)

새로운 배열

Website [] websites = new Website[20]; 

로 채워 때문에 당신은 java.lang.NullPointerException을 받고있어 배열

for(int i=0; i < 10; i++)