I'm writing a List ADT where I will be able to add/remove items anywhere in the list unlike (Stacks and Queues). I also want to be able to iterate through the list. So I'm creating pointers to keep track of items.When I try to add items in the list (in test harness class) I get a bound miss-match.
Please take a look at the interface below I think you will be able to get a better idea.
package List;
public interface ListInterface < ObjectType extends KeyInterface > extends Iterable<ObjectType> {
public void add ( ObjectType item ); // adds item in front of the key
public ObjectType remove ( ); // returns item at the key and removes it
public ObjectType get ( ); // returns item at the key
public boolean empty ( ); // returns boolean // check for empty
public int length ( ); // length of the list
public void toFront ( ); // moves pointer to the front of the list
public void advance( ); // moves the pointer to the next item
public void find ( String key ); // pointer finds the input key
public boolean offEnd ( ); // returns true if pointer is off the list
}
Using a bounded type parameter to make ObjectType a subtype of KeyInterface
Below is the KeyInterface
package List;
public interface KeyInterface {
public String getKey ( ); // Returns the Key of the item
}
Here's how my List implementation looks like.
package List;
import java.util.Iterator;
public class ListImplementation < ObjectType extends KeyInterface > implements ListInterface<ObjectType> {
ObjectType[] items; // the items in the list
int cursor; // the list cursor
int length; // the length of the list
public ListImplementation() {
this(100);
}// constructor
public ListImplementation(int size) {
items = (ObjectType[]) new KeyInterface[size];
cursor = 0;
length = 0;
}// constructor
@Override
public Iterator<ObjectType> iterator() {
return new ListIterator<ObjectType>(this);
}
@Override
public void add(ObjectType item) {
int j;
if ( length >= items.length ) {
throw new NullPointerException();
}
else {
for ( j = length-1 ; j>=cursor ; j-- ) {
items[j+1] = items[j];
}
items[cursor] = item;
length = length + 1;
}
}
@Override
public ObjectType remove() {
ObjectType i;
int j;
if ( cursor >= length ) {
throw new NullPointerException();
}
else {
i = items[cursor];
for ( j=cursor+1 ; j<length ; j++ ) {
items[j-1] = items[j];
};
length = length-1;
items[length] = null;
return i;
}
}
@Override
public ObjectType get() {
if ( cursor >= length ) {
throw new NullPointerException();
}
else {
return items[cursor];
}
}
@Override
public boolean empty() {
return length == 0;
}
@Override
public int length() {
return length;
}
@Override
public void toFront() {
cursor = 0;
}
@Override
public void advance() {
if ( cursor < length ) {
cursor = cursor + 1;
}
}
@Override
public void find(String key) {
while ( cursor < length && key.compareTo(items[cursor].getKey()) != 0 ) {
cursor = cursor + 1;
}
}
@Override
public boolean offEnd() {
return cursor >= length;
}
}
Logically I don't see any errors in this class and I have tested the methods separately. Also made a List Iterator class to for iterating through the List. This is how it looks like.
public class ListIterator<ObjectType extends KeyInterface > implements Iterator<ObjectType> {
private int cursor; // the cursor that iterates through the list
private ListImplementation <ObjectType> list; // the list being iterated over
ListIterator ( ListImplementation <ObjectType> l ) {
list = l;
cursor = 0;
}; // constructor
@Override
public boolean hasNext() {
return cursor < list.length;
}
@Override
public ObjectType next() {
ObjectType i;
if ( cursor >= list.length ) {
throw new NoSuchElementException();
}
else {
i = list.items[cursor];
cursor = cursor + 1;
return i;
}
}
@Override
public void remove() {
throw new UnsupportedOperationException(); // Doesn't do anything
}
}
I know the remove method is doing nothing a its a bad design, please ignore it for now. Now I'm stuck in the test Harness part. I don't know how can I add different items since there are so many extends in class.
public static void main(String args[]){
ListImplementation < String> ls = new ListImplementation < String>();
}
whatever I put inside <> turns out to be a bound mismatch.so what could be a valid substitute for the bounded parameter. Help??
