Prefix to Expression tree

[scottmulla]

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.

files.zip

[scottmulla]

so far i have this

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;}
			}
		}
	}	
	
	
}

[david522]

Bump, need help with this too.

[JosAH]

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

[scottmulla]

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