访问树java中的各个节点

Question

I am making a class ExpTree which includes a method to generate pre order output and return this as a string. So far I have the basic code to make the tree but I am not sure how to write to pre order method.

I have tried to access the tree data by making an ExpTree object in the main method, and then in my preorder method writing 'x.root' in a print statement. This however would return 'ExpTree.OperatorNode@7637f22'. When ideally I was hoping that it would return some of the values that are in the tree.

I am a beginner to trees in java so if someone could perhaps explain what I need to do here that would be great!

Thanks

EDIT - If it isnt clear, what I am asking is that I want to be able to order the Exp trees that are supplied to the method 'preorder' using the preorder traversal. The output of this method should be as a string.

The problem is that I dont know how to access the potential parts of the ExpTree so I am unable to order them.

Answer 1

You do not need char expression in your leafNode. leafNode can be just integers and the OperatorNode has the leafNodes (integers) and expression char.

public static void main(String[] args)
{

    ExpTree tree = new ExpTree('*', 1 , 2);
    System.out.println(tree.preOrder());

}

//Class Exp Tree creates Expression Tree with method to generate pre order output.

package ExpTree;


public class ExpTree {

    public Node root;

    public ExpTree ( char x, int y, int z){

        this.root = new OperatorNode(x, y, z);
    }

    public String preOrder (){

        return root.preOrder();
    }

}

abstract class Node {
    public abstract String preOrder();
}

class OperatorNode extends Node {

    char operator;
    Node left;
    Node right;

    public OperatorNode(char x, int y, int z){

        this.operator = x;
        this.left = new leafNode (y);
        this.right = new leafNode (z);
    }

    public String preOrder() {
        return this.operator + this.left.preOrder() + this.right.preOrder();
    }

}

class leafNode extends Node{
    int value;

    public leafNode(int x){
         this.value = x;
    }

    public String preOrder() {
        return Integer.toString(this.value);
    }
}