How do you declare an array where user can specify dimension?

I want a function / data structure that can do th开发者_JS百科is:

func(int dim){

if(dim == 1)

int[] array;

else if (dim == 2)

int[][] array;

else if (dim == 3)

int[][][] array;

..

..

.

}

anyone know how?

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Edit

Or you could use Array.newInstance(int.class, sizes). Where sizes is an int[] containing the desired sizes. It will work better because you could actually cast the result to an int[][][]...

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Original Answer

You could use the fact that both int[] and Object[] are Objects. Given that you want a rectangular multidimensional array with sizes given by the list sizes

Object createIntArray(List<Integer> sizes) {
    if(sizes.size() == 1) {
        return new int[sizes.get(0)];
    } else {
        Object[] objArray = new Object[sizes.get(0)];
        for(int i = 0; i < objArray.length; i++) {
           objArray[i] = createIntArray(sizes.subList(1, sizes.size());
        }
        return objArray;
    }
}

You lose all static type checking, but that will happen whenever you want a dynamically dimensioned array.

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If your purpose is to create a truly dynamic array, then you should look at the Array object in the JDK. You can use that to dynamically generate an array of any dimension. Here is an example:

    public void func(int dim) {
        Object array = Array.newInstance(int.class, new int[dim]);
        // do something with the array        
    }

Once the array Object has been created, you can use the methods of the java.lang.reflect.Array class to access, add, remove elements from the multi-dimension array that was created. In also includes utility methods to determine the length of the array instance.

You can even check the dimension of the array using:

public int getDimension(Object array) {
    int dimension = 0;
    Class cls = array.getClass();
    while (cls.isArray()) {
        dimension++;
        cls = cls.getComponentType();
    }
    return dimension;
}

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People have post good solutions already, but I thought it'd be cool (and good practice) if you wrap the dynamic multidimensional array into a class, which can use any data structure to represent the multi-dimensional array. I use hash table so you have virtually unlimited size dimensions.

public class MultiDimArray{
  private int myDim;
  private HashMap myArray;

  public MultiDimArray(int dim){
     //do param error checking 
     myDim = dim;
     myArray= new HashMap();
  }

  public Object get(Integer... indexes){
     if (indexes.length != myDim){throw new InvalidArgumentException();}

     Object obj = myArray;
     for (int i = 0; i < myDim; i++){
       if(obj == null)
         return null;

         HashMap asMap = (HashMap)obj;
         obj = asMap.get(indexes[i]);
     }

     return obj;
  }

  public void set(Object value, Integer... indexes){
    if (indexes.length != myDim){throw new InvalidArgumentException();}
      HashMap cur = myArray;
      for (int i = 0; i < myDim - 1; i++){
        HashMap temp = (HashMap)cur.get(indexes[i]);
        if (temp == null){
          HashMap newDim = new HashMap();
          cur.put(indexes[i], newDim);
          cur = newDim;
        }else{
          cur = temp;
        }
     }
     cur.put(indexes[myDim -1], value);
  }
}

and you can use the class like this:

Object myObj = new Object();
MultiDimArray array = new MultiDimArray(3);
array.put(myObj, 0, 1, 2); 
array.get(0, 1, 2); //returns myObj
array.get(4, 5, 6); //returns null

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What about a class like following?

class DynaArray {

private List<List> repository = new ArrayList<List>();

public DynaArray (int dim) {
for (int i = 0; i < dim; i++) {
     repository.add(new ArrayList());
}
}

public List get(int i) {
return repository.get(i);
}

public void resize(int i) {
 // resizing array code
}

}