Question

While using method Arrays.deepToString(Object [] a) I am facing this problem which I can put down in this way.

 Object [] not_allowed = new  int[]{7, 9, 8};
 Object [] allowed  = new int[][]{{1, 2, 3}, {6, 5, 4}};

Why i am not allowed to assign int[] to Object[] in single dimension case but i am allowed to do such in multidimension case.

Answer 1

Primitive types like int are not Objects while an array is an Object– you can assign any array to an Object reference

Object o = new  int[]{7, 9, 8};

new int[][] is an array of objects and thus can be assigned to Object[]. You may want to write a utility method like this to do what you want:

public static String arrayToString(Object o) {
    if(o instanceof Object[])  {
        return Arrays.deepToString((Object[]) o);
    }
    else if(o instanceof long[]) {
        return Arrays.toString((long[]) o);
    }
    else if(o instanceof int[]) {
        return Arrays.toString((int[]) o);
    }
    else if(o instanceof short[]) {
        return Arrays.toString((short[]) o);
    }
    else if(o instanceof byte[]) {
        return Arrays.toString((byte[]) o);
    }
    else if(o instanceof float[]) {
        return Arrays.toString((float[]) o);
    }
    else if(o instanceof double[]) {
        return Arrays.toString((double[]) o);
    }
    else if(o instanceof boolean[]) {
        return Arrays.toString((boolean[]) o);
    }
    throw new IllegalArgumentException("input is not an array");
}

Example:

Object intArray = new  int[]{7, 9, 8};
Object[] intintArray  = new int[][]{{1, 2, 3}, {6, 5, 4}};
Object[] intintintArray  = new int[][][]{{{1, 2, 3}, {6, 5, 4}},
               {{1, 2, 3}, {6, 5, 4}}};
System.out.println(arrayToString(intArray));
System.out.println(arrayToString(intintArray));
System.out.println(arrayToString(intintintArray));

Output:

[7, 9, 8]
[[1, 2, 3], [6, 5, 4]]
[[[1, 2, 3], [6, 5, 4]], [[1, 2, 3], [6, 5, 4]]]