使用類方法在ArrayList中查找類似的整數

Question

我需要遍歷對象和ArrayList對象並查找具有多個對象相同值的變量。如下面的例子，我正在瀏覽一個ArrayList，它有一個子類。我想要做的是找出一個房子或公寓共享這個示例代碼相同的列表號碼。我嘗試使用雙循環，並使用方法（sameListingNum）進行增強循環，並且無法解決問題。

謝謝

// main client class 
public static void main(String[] args) 
    { 
     ArrayList<House> listings = new ArrayList(); 

     listings.add(new House(0001, 200000.00)); 
     listings.add(new House(0201, 200000.00)); 
     listings.add(new House(0001, 200000.00)); 
     listings.add(new House(0401, 200000.00)); 
     listings.add(new House(0031, 200000.00)); 
     listings.add(new Condo(0401, 200000.00, 4)); 
     listings.add(new Condo(0001, 120000.00, 3)); 
     listings.add(new Condo(0301, 220000.00, 2)); 
     listings.add(new Condo(0001, 130000.00, 3)); 
     listings.add(new Condo(0201, 130000.00, 3)); 

     for(House currentHouse: listings) 
     System.out.println(currentHouse); 
     for(int i=0; i<listings.size()-1; i++) 
     { 
     for(int j=i+1; j<listings.size(); j++) 
     { 

     } 
     } 

// House Class 
public class House 
{ 
    public int listingNum; 
    public double price; 

    public House() 
    { 
    listingNum = 0; 
    price = 0.00; 
    } 
    public House(int newListingNum, double newPrice) 
    { 
    listingNum = newListingNum; 
    price = newPrice; 
    } 
    public int getListingNum() 
    { 
    return listingNum; 
    } 
    public double getPrice() 
    { 
    return listingNum; 
    } 
    public String toString() 
    { 
    return ("Listing number: "+listingNum+", Price: "+price); 
    } 
    public boolean sameListingNum(Object other) 
    { 
    if(!(other instanceof House)) 
     return false; 
    else { 
     House objHouse = (House)other; 
     if(listingNum - objHouse.getListingNum() == 0) 
     { 
     System.out.println("Same listing numbers: " 
     +listingNum+", "+objHouse.getListingNum()); 
     return true; 
     } 
     else 
     return false; 
    } 
    } 
} 

// Condo Class 
public class Condo extends House 
{ 
    public int connectedUnits; 

    public Condo() 
    { 
    super(); 
    connectedUnits = 0; 
    } 
    public Condo(int newListingNum, double newPrice, int newConUnits) 
    { 
    super(newListingNum, newPrice); 
    connectedUnits = newConUnits; 
    } 

    public double getPrice() 
    { 
    return price; 
    } 
    public int getListingNum() 
    { 
    return listingNum; 
    } 
    public int getConnectedUnits() 
    { 
    return connectedUnits; 
    } 
    public String toString() 
    { 
    return super.toString()+", Number of connected unints: "+connectedUnits; 
    } 

public boolean sameListingNum(Object other) 
      { 
      if(!(other instanceof House)) 
       return false; 
      else { 
       House objHouse = (House)other; 
       if(listingNum - objHouse.getListingNum() == 0) 
       { 
       System.out.println("Same listing numbers: " 
       +listingNum+", "+objHouse.getListingNum()); 
       return true; 
       } 
       else 
       return false; 
      } 
     } 

Answer 1

您可以將它用列表的地圖，像地圖>組。

然後你循環你的名單和每個房子/公寓你把它放在同一個列表編號的組中。最後，你會得到一個地圖，每個入口都有相同房產號碼的房屋/公寓。

這裏的樣本：

Map<Integer, List<House>> groups = new HashMap<Integer, List<House>>(); 
for (House house:listings) { 
    List<House> group = groups.get(house.getListingNum()); 
    if (group == null) { 
    group = new ArrayList<House>(); 
    groups.put(house.getListingNum(), group); 
    } 
    group.add(house); 
} 

for (Entry<Integer, List<House>> entry:groups.entrySet()) System.out.println("Listing Number "+entry.getKey()+" Houses/condos: "+entry.getValue()); 

Answer 2

試試這個：

foreach(House h in listings) 
{ 
if(listings.Exists(p => p.sameListingNum(h))) 
{ 
//do something 
} 
} 

Answer 3

其他2個答案都將alternativly工作，你可以實現在衆議院可比...如。

public class House implements Comparable<House> 

@Override 
public int compareTo(final House o) { 
    return listingNum - o.listingNum; 
} 

然後在你的主要方法。對收藏集進行排序，並檢查前一行是否始終具有相同的ID。

Collections.sort(listings); 

    int previousListing = Integer.MIN_VALUE; 

    for (House currentHouse : listings) { 
     if (currentHouse.getListingNum() == previousListing){ 
      System.out.println("Duplicate for " + currentHouse.getListingNum()); 
     } 
     previousListing = currentHouse.getListingNum(); 
    } 

請選擇。