式ツリー

import java.util.Stack;

/**
 *     
 */
public class ExpTree {
	
	/**       */
	public static TNode<Character> buildExpTree(String postfixExp) {
		char c;
		TNode<Character> newNode, newLeft, newRight;
		Stack<TNode<Character>> s = new Stack<TNode<Character>>();
		int i = 0, len = postfixExp.length();
		
		while(i != len) {
			while(postfixExp.charAt(i) == ' ' || postfixExp.charAt(i) == '\t')
				i++;
			
			if(i == len)
				break;
			c = postfixExp.charAt(i);
			i++;
			
			if(c == '+' || c == '-' || c == '*' || c == '/') {
				newRight = s.pop();
				newLeft = s.pop();
				
				newNode = new TNode<Character>(c, newLeft, newRight);
				s.push(newNode);
			} else {
				newNode = new TNode<Character>(c);
				s.push(newNode);
			}
		}
		
		if(! s.isEmpty())
			return s.pop();
		else
			return null;
	}
	
	/**    */
	public static <T> void inorderOutput(TNode<T> t) {
		if (t != null) {
			inorderOutput(t.getLeft());
			System.out.print(t.getKey() + " ");
			inorderOutput(t.getRight());
		}
	}

	public static void main(String[] args) {
		String exp = "abc*+";
		TNode<Character> root = ExpTree.buildExpTree(exp);
		ExpTree.inorderOutput(root); // a + b * c
	}

}

package edu.cumt.jnotnull;

public class TNode<T> {
	private T key;
	private TNode<T> left, right;

	public TNode(T key) {
		this(key, null, null);
	}

	public TNode(T key, TNode <T>left, TNode<T> right) {
		this.key = key;
		this.left = left;
		this.right = right;
	}

	public T getKey() {
		return key;
	}

	public void setKey(T key) {
		this.key = key;
	}

	public TNode<T> getLeft() {
		return left;
	}

	public void setLeft(TNode<T> left) {
		this.left = left;
	}

	public TNode<T> getRight() {
		return right;
	}

	public void setRight(TNode<T> right) {
		this.right = right;
	}
}