比较Java数组

Question

I'm trying to compare the names of the roomtypes in a simple Java program but I can't get it to work.

So far I have this:

public class Main {
public static void main(String[] args) {
    RoomType[] ar = new RoomType[10];
    String s = "";
    String duplicate = "";

    ar[0] = new RoomType("Standaard", 2, 60.0);
    ar[1] = new RoomType("DeLuxe", 2, 85.0);
    ar[2] = new RoomType("DeLuxe", 4, 125.0);
    ar[3] = new RoomType("Hiker", 2, 35.0);

    for (int i = 0; i < ar.length; i++) {
        if (ar[i] != null) {
            s += ar[i] + "\n";
        }

        for (int j = 0; j < ar.length -1; j++) {
            if (ar[i] == ar[j] && ar[i] != null && ar[j] != null) {
                duplicate = ar[i] + " has the same name as " + ar[j];
            }
        }
    }

    System.out.println("These are the roomtypes: \n" + s + "\n");
    System.out.println(duplicate);
}

}

I want to compare the names (the first elements in the arrays) of all ar[] 's and if there are doubles I need a sysout that gives the position ( ar[] ) of the doubles. The method getTypeName() is in a different class RoomType.

Answer 1

"I want to compare the names (the first elements in the arrays) of all ar[]'s and if there are doubles I need a sysout that gives the position (ar[]) of the doubles"

It seems like your approach is wrong. Your RoomType could implement equals and hashcode based on your requirements and then you can add them to a data structure that doesn't permit duplicates like java.util.Set . Trying to insert a duplicate element to a Set will return false and this could help you. Unless you are practicing/playing around with arrays in Java, standard data structures will solve these kind of problems for you.

Answer 2

A couple of things to note:

• It is far more space/time efficient to use a StringBuilder : http://docs.oracle.com/javase/7/docs/api/java/lang/StringBuilder.html to "grow" Strings.
• "==" and "!=" compare Strings by reference instead of value. Use .equals() instead.
• We can use a HashMap<String, ArrayList<Integer>> to efficiently store duplicate info. We map type names to positions in the array. I've written a function below:

---

public void printDuplicateInfo(RoomType[] roomList) {

  HashMap<String, ArrayList<Integer>> map = new HashMap<String, ArrayList<Integer>>();
  for(int i = 0; i < roomList.length; i++) {
    ArrayList<Integer> pos;
    String name = roomList[i].getTypeName()
      if(!map.containsKey(name))
        pos = new ArrayList<Integer>();
      else
        pos = map.get(name);
    pos.add(i);
    map.put(name, pos);
  }

  Set<String> keys = map.keySet();
  StringBuilder strBuf = new StringBuilder();
  strBuf.append("***Duplicate Info***\n");
  for(String name : set) {
    ArrayList<Integer> pos = map.get(name);
    int size = pos.size();
    if(size == 1)
      continue;
    strBuf.append(name).append(": present at indices ");
    for(int i = 0; i < size; i++)
      strBuf.append(pos.get(i)).append(" ");

    strBuf.append("\n")
  }

  System.out.print(strBuf);
}

Answer 3

Here is what I interpreted as what you are asking for:

for(int i = 0; i < ar.length; i++)
{
  if(ar[i] != null)
    s += ar[i].getTypeName()+"\n";
 for(int j = 1; j < ar.length; j++)
  {
    if(ar[i] != null && ar[j] != null && ar[i].getTypeName().equals(ar[j].getTypeName()))
    {
        duplicate += i+" has the same name as "+j+"\n";
    }
  }
}
System.out.println("These are the roomtypes: \n"+s+"\n");
System.out.println(duplicate);

Answer 4

Try using ArrayList, and .Contains to compare. It will make your life easier and get you introduced to more datastructures in Java.

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