What does the question mark and the semi-colon do in the following code

Question

public void set(int index, Object value) {
    int j;          // loop index
    int newLength;  // new size of array, if required
    if ( index < 0 )
      throw new ArrayIndexOutOfBoundsException(index);
    else {
      if ( index >= objs.length ) {
        resize(index) ;
      } // end if
      if ( index >= size ) {
        size = index + 1;
      objs[index] = ( value == null ? NULL_OBJ : value ) ;   } // end else
  } // end set

Answer 1

Read about the ternary operator at http://java.sun.com/docs/books/tutorial/java/nutsandbolts/operators.html