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Java Data Structures - Contents


Nodes...

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    The other type of data structures are what's called Node based data structures. Instead of storing data in it's raw format, Node based data structures store nodes, which in turn store the data. Think of nodes as being elements, which may have one or more pointers to other nodes.

    Yes, I did say the "pointer" word. Many people think that there are no pointers in Java, but just because you don't see them directly, doesn't mean they're not there. In fact, you can treat any object as a pointer.

    Thus, the Node structure should have a data element, and a reference to another node (or nodes). Those other nodes which are referenced to, are called child nodes. The node itself is called the parent node (or sometimes a "father" node) in reference to it's children. (nice big happy family)

    Well, the best way to visualize a node is to create one, so, lets do it. The node we'll create will be a one child node (it will have only one pointer), and we'll later use it in later sections to build really cool data structures. The source for our one child node follows:

public class pOneChildNode{
    protected Object data;
    protected pOneChildNode next;

    public pOneChildNode(){
        next = null;
        data = null;
    }
    public pOneChildNode(Object d,pOneChildNode n){
        data = d;
        next = n;
    }
    public void setNext(pOneChildNode n){
        next = n;
    }
    public void setData(Object d){
        data = d;
    }
    public pOneChildNode getNext(){
        return next;
    }
    public Object getData(){
        return data;
    }
    public String toString(){
        return ""+data;
    }
}

    Go over the source, notice that it's nothing more than just set and get functions (pretty simple). The two data members are the data and next. The data member holds the data of the node, and next holds the pointer to the next node. Notice that next is of the same type as the class itself; it effectively points to the object of same class!

    The String toString() method is the Java's standard way to print things. If an object wants to be printed in a special way, it will define this method, with instructions on how to print this object. In our case, we just want to print the data. Adding data to a bunch of quotation marks automatically converts it to type String (hopefully, our data will also have a toString() method defined on it). Without this method, we get the actual binary representation of the data members of this class (not a pretty nor meaningful printout).

    Node based data structures provide for dynamic growing and shrinking, and are the key to some complex algorithms (as you'll see later). Now that we know how to implement a Node, lets get to something cool...


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