Prefix to Expression tree

I am trying to make a basic java program that takes an infix expression as the argument (i.e. "+ * 2 - 7 3 / 20 5") and outputs it as an arithmetic expression tree and evaluates the tree.

i have the attached classes to work with...am really struggling on this one so any help would be appreciated.

Attachment 1877

so far i have this

Code:

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public class ArithmeticTreeTest {
       
        public static void main(String[] args) throws IOException {
                BinaryTreeNode tree = null;
                String preFix = args[0];
                StringTokenizer st = new StringTokenizer(preFix);       


                while (st.hasMoreTokens()){
                        String tokens = st.nextToken();
                        System.out.println(tokens);
                        try{
                                int num = Integer.parseInt(tokens);
                                if (tree.left() == null){
                                        tree.setLeft(new BinaryTreeNode(new Integer(num)));
                                } else {
                                        tree.setRight(new BinaryTreeNode(new Integer(num)));
                                }
                        } catch (NumberFormatException e){
                                char operator = tokens.charAt(0);
                                tree = new BinaryTreeNode(operator, null, null);
                        }
                }

                System.out.println();
                System.out.println("The tree representation is:");
                System.out.println(tree.toString());
                System.out.println();
                System.out.println("The tree evaluates to " + evaluate(tree));
                System.out.println();
        }
       
        protected static int evaluate(BinaryTreeNode node){
                if (BinaryTreeNode.size(node)==1)
                        return ((Integer) node.value()).intValue();
                else {
                        int left=evaluate(node.left());
                        int right=evaluate(node.right());
                        char c=((Character) node.value()).charValue();
                        switch (c){
                                case '+': return (left+right);
                                case '*': return (left*right);
                                case '-': return (left-right);
                                case '/': return (left/right);
                                case '%': return (left%right);
                                default: { System.out.println("Unknown operator!");
                                                        System.exit(-1); return 0;}
                        }
                }
        }       
       
       
}

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Bump, need help with this too.

Maybe you'll find one of my blog articles useful; it babbles about expression compilation and the code can do what you want (and some more).

kind regards,

Jos

Thanks for the help, that's all a bit advanced for me i don't really understand most of it...