ArrayList中的問題<Integer>

Question

import java.util.*; 
import java.util.Random; 

class ArraySorting { 
public static void main(String[]args) { 

    ArrayList<Integer> arr = new ArrayList<Integer>(); 

    Random generate = new Random(); 
    for (int nums = 0; nums < 20; nums++) { 
     int randomnumbers = generate.nextInt(50); 
     arr.add(randomnumbers); 
    } 

    System.out.println("First list of 20 generated numbers: "); 
    System.out.println(arr); 
    System.out.println(""); 

    int dupe = 0; 

    for (int n = 0; n < arr.size(); n++) { 
     Integer check1 = arr.get(n); 

     for (int n2 = n+1; n2 < arr.size(); n2++) { 
      Integer check2 = arr.get(n2); 

      //remove second num if two numbers akike 
      if (check1.equals(check2)) { 
       arr.remove(check2); 
       n2 = n2-1; 
       dupe = 1; 

      } 
     } 
     n = n-dupe; 
     dupe = 0; 
    } 

    System.out.println("Duplicates: " + (20 - arr.size())); 

    for (int n3 = arr.size(); n3 < 20; ++n3) { 
     int randomnumbers = generate.nextInt(50); 
     arr.add(randomnumbers); 

     //check for duplicates again 
     for (int n = 0; n < arr.size(); n++) { 
      Integer check1 = arr.get(n); 

      for (int n2 = n+1; n2 < arr.size(); n2++) { 
       Integer check2 = arr.get(n2); 

       if (check1.equals(check2)) { 
        arr.remove(check2); 
        n2 = n2-1; 
        dupe = 1; 
       } 
      } 
      n = n - dupe; 
      dupe = 0; 
     } 
    } 

    //before sort 
    System.out.println(arr); 
    System.out.println(""); 

    for(int a=0; a<20; a++){ 
     for (int b = 0; b < 19; b++) { 
      if(arr[b] > arr[b+1]){ 
       int temporary = arr[b]; 
       arr[b] = arr[b+1]; 
       arr[b+1] = temporary; 
      } 
     } 
    } 

    System.out.println("\nSorted Array:\n"); 
    for (int a = 0; a < 20; a++) { 
     System.out.println("Array [" + a + "]: " + arr[a]); 
    } 


} 

} 

任何人都可以告訴我我爲此做了什麼錯誤，但似乎無法生成最後一部分。不應該ArrayList arr = new ArrayList（）;運行與arr [b]工作的最後部分相同？我是Java的新手，所以如果簡單的解釋/隱喻是隨解決方案提供的，我將非常感激。

P.S：我不打算使用像Collection這樣的庫函數，我需要在最後一部分使用排序方法。

Answer 1

arr[a]是訪問數組元素的語法。對於ArrayList，您可以使用arr.get(a)。並且要爲ArrayList分配一個值，則使用arr.set(b,value)。您不能使用賦值運算符。

Answer 2

您遇到的問題是您正在嘗試在排序前刪除重複項。首先，整理你的整數，重複和全部，然後刪除重複項。

import java.util.ArrayList; 
import java.util.Random; 

public class ArraySorting { 
    public static void main(String[]args) { 

     ArrayList<Integer> arr = new ArrayList<Integer>(); 

     Random generate = new Random(); 
     for (int nums = 0; nums < 20; nums++) { 
      int randomnumbers = generate.nextInt(10); 
      arr.add(randomnumbers); 
     } 

     System.out.println("First list of 20 generated numbers: "); 
     System.out.println(arr); 
     System.out.println(""); 

     // SORT YOUR LIST FIRST 
     bubbleSort(arr); 
     System.out.println(arr); 

     // NOW YOU CAN REMOVE YOUR DUPLICATES 
     removeDuplicates(arr); 
     System.out.println(arr); 
    } 

    public static void bubbleSort(ArrayList<Integer> list){ 
     for(int i = 0; i < list.size(); i++) { 
      for(int j = 1; j < (list.size() -i); j++) { 
       if(list.get(j - 1) > list.get(j)) { 
        int temp = list.get(j-1); 
        list.set(j-1, list.get(j)); 
        list.set(j, temp); 
       }     
      } 
     }  
    } 

    public static void removeDuplicates(ArrayList<Integer> list){ 
     for(int i = 0; i < list.size(); i++) { 
      if(i < list.size()-1) { 
       int prev = list.get(i); 
       int curr = list.get(i + 1); 

       if(curr == prev) { 
        list.remove(list.get(i + 1)); 
        i--; 
       } 
      } 
     } 
    } 
} 

輸出

First list of 20 generated numbers: 
[9, 2, 2, 1, 3, 4, 0, 9, 5, 2, 5, 7, 4, 9, 0, 4, 0, 6, 6, 6] 

[0, 0, 0, 1, 2, 2, 2, 3, 4, 4, 4, 5, 5, 6, 6, 6, 7, 9, 9, 9] 
[0, 1, 2, 3, 4, 5, 6, 7, 9]