How To Add New Element Into An Array

I need to port code from blackberry to android and facing small problem: Example: the bb code is: public class MyClass{ private MyObject[] _myObject; public void addElement(

Solution 1:

Yes, because the _myObject reference is passed by value. You'd need to use:

publicstaticObject[] add(Object[] array, Objectobject){
  ArrayList<Object> lst = newArrayList<Object>();
  for (Object o : array){
    lst.add(o);
  }
  lst.add(object);
  return lst.toArray();
}

...

_myObject = Arrays.add(_myObject, o);

However, it would be better to just use an ArrayList<E> to start with...

There are two important things to understand here:

Java always uses pass-by-value

The value which is passed is either a reference (a way of getting to an object, or null) or a primitive value. That means if you change the value of the parameter, that doesn't get seen by the caller. If you change the value of something within the object the parameter value refers to, that's a different matter:

voiddoSomething(Person person) {
  person.setName("New name"); // This will be visible to the caller
  person = newPerson(); // This won't
}

Arrays are fixed-size in Java

You can't "add" a value to an array. Once you've created it, the size is fixed. If you want a variable-size collection (which is a very common requirement) you should use an implementation of List<E> such as ArrayList<E>.

Solution 2:

• commons-lang has ArrayUtils.add(..)
• guava has ObjectArrays.concat(..).

Here's the code of ObjectArrays.concat(object, array):

publicstatic <T> T[] concat(@Nullable T element, T[] array) {
    T[] result = newArray(array, array.length + 1);
    result[0] = element;
    System.arraycopy(array, 0, result, 1, array.length);
    return result;
  }

The apache-commons code is a bit longer.