Suppose you have an array of some type that is full, and you
want to grow it.
Employee[] a = new Employee[100];
// array is full
int newLength = a.length * 11 / 10 + 10;
Employee[] newArray = new Employee[newLength];
System.arraycopy(a, 0, newArray, 0, a.length);
a = newArray;
That gets boring really quickly. Let's try to make it generic.
static Object[] arrayGrow(Object[] a) // not usefull
{
int newLength = a.length * 11 / 10 + 10;
Object[] newArray = new Object[newLength];
System.arraycopy(a, 0, newArray, 0, a.length);
return newArray;
}
Problem: Return type is Object[], not Employee [] .
a = (Employee[]) arrayGrow(a); // throws ClassCastException.
Tip
Use reflection to make a new array of the same type:
static Object arrayGrow(Object a) // useful
{ Class cl = a.getClass(); if (!cl.isArray()) return null;
int length = Array.getLength(a);
int newLength = length * 11 / 10 + 10;
Class componentType = a.getClass().getComponentType();
Object newArray = Array.newlnstance(componentType, newLength);
System.arraycopy(a, 0, newArray, 0, length);
return newArray;
}
Typical usage:
Employee[] a = new Employee[100]; . . . . .// array is full
a = (Employee[]) arrayGrow(a);
Note
This arrayGrow method can be used to grow arrays of any type, not just arrays
of objects.
int[] ia = ( 1, 2, 3, 4 };
ia = (int[])arrayGrow(a);
Note that the parameter of arrayGrow is declared to be of type object, not an
array of objects
(Object [] ). The integer array type int [] can be converted to an object, but
not to an array of objects!
