Multi-Dimension length array reflection java

Question

How do I find the length of a multi-dimensional array with reflection on java?

Answer 1

Class clazz = Class.forName("ReflectionTest");    
Method m = clazz.getDeclaredMethod("getArray");
Object o1 = m.invoke(o, arg);
int array[][] = (int[][])o1;
System.out.println("Array length: " + array.length);
System.out.println("Array length: " + array[0].length);

Answer 2

Use java.lang.reflect.Array.getLength(obj).

Answer 3

There is no such thing as "length" for multi-dimensional array; it may not be rectangular. I'm guessing you're talking about the number of dimensions. You need to descend into it iteratively and count.

public int getDimensionCount(Object array) {
  int count = 0;
  Class arrayClass = array.getClass();
  while ( arrayClass.isArray() ) {
    count++;
    arrayClass = arrayClass.getComponentType();
  }
  return count;
}

Answer 4

Java arrays have lengths per instance, not all arrays in the same dimension have to have equals lengths. That said, you can get the lengths of instances in the.

Dimensions can be counted by the number of '[' in their name, this is quicker than descending the type hierarchy. The following code:

  int[][][] ary = {{{0},{1}}};

  Class cls = ary.getClass();

  boolean isAry = cls.isArray();
  String clsName = cls.getName();

  System.out.println("is array=" + isAry);
  System.out.println("name=" + clsName);

  int nrDims = 1 + clsName.lastIndexOf('[');

  System.out.println("nrDims=" + nrDims);

  Object orly = ary;

  for (int n = 0; n < nrDims; n++) {

   int len = Array.getLength(orly);

   System.out.println("dim[" + n + "]=" + len);

   if (0 < len) {
    orly = Array.get(orly, 0);
   }
  }

gives the following output:

is array=true
name=[[[I
nrDims=3
dim[0]=1
dim[1]=2
dim[2]=1