For loop with a generic array?
Going back over my basic ADT stuff here, and trying to kill two birds with one stone by learning Java while I amTrying to write a simple algorithm for a merge sort with a generic linked list ( which I am creating myself). It's proving to be far more difficult than I had first imagined ! Can anyone help me out please ? I will start out working on the basics and will update this post as I get further in.
My code for the generic linked list is as follows :
public class NodeList<T> {
private Comparable head;
private NodeList tail;
public NodeList( Comparable item, NodeList list ) {
head = item;
tail = list;
}
}
I am trying to access this class in another class I have made, which is as follows :
public class MyList<T> {
private NodeList<T> nodes;
private int size;
public MyList( ) {
nodes = null;
}
public MyList(T[] array ){
for(int countArray = 0; countArray <= array.length() ; countArray++) {
nodes= new NodeList( value, nodes );
size++;
}
}
which should add generic items from an array, using a linked list. Unfortunately, it doesn't and this is the first problem I have encountered. I am getting the error :
cannot find symbol : method length().
Can someone give开发者_开发知识库 me some advice on how I could fix this?
Many thanks!
on the array you don't have a length() method but a length member : array.length
Additionally, you'll want to stop iterating before countArray reaches array.length and initialise size before using it:
final int arrayLength = array.length;
size = arrayLength;
nodes = null;
for(int i = 0; i < arrayLength; ++i) {
nodes = new NodeList(array[i], nodes);
}
or
nodes = null;
size = array.length;
for(T element : array) {
nodes = new NodeList(element, nodes);
}
The method on a collections class is .size()
, or on an array it is the .length
property.
But you can loop through either of these with an "enhanced" for loop (aka foreach):
for( T element : array ) {
nodes = new NodeList( value, nodes );
size++;
}
In addition to what others have posted, you might also want to use your generic parameter T:
public class NodeList<T> {
private T head;
private NodeList<T> tail;
public NodeList( T item, NodeList list ) {
head = item;
tail = list;
}
}
length
is a field, not a method, on arrays. Remove the parentheses.
for(int countArray = 0; countArray <= array.length ; countArray++) {
nodes= new NodeList( value, nodes );
size++;
}
Here's a better way to write the whole constructor:
public MyList(T[] array ){
nodes = null;
for(T t : array) {
nodes = new NodeList(t, nodes);
}
size = array.length;
}
If you want to make sure that only comparable items are possible:
public class NodeList<T extends Comparable<T> > {
private T head;
private NodeList<T> tail;
public NodeList( T item, NodeList<T> list ) {
head = item;
tail = list;
}
}
And
public class MyList<T extends Comparable<T>> {
...
}
Additionally, if your constructor uses var args, you get a more convenient way of creating a list:
public MyList(T... array ) {
for( T item : array ) {
nodes = new NodeList<T>(item, nodes);
}
size = array.length;
}
That way you can call the constructor as follows:
new MyList<Long>(); //empty list
new MyList<Long>( 1L ); //one entry
new MyList<Long>( 1L, 2L, 3L ); //3 entries
Long[] array = new Long[] { 1L, 2L, 3L, 4L };
new MyList<Long>( array ); //use existing array
It is array.length not array.length().
for(int countArray = 0; countArray <= array.length ; countArray++) {
will resolve your compilation error.
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