A simple implementation of "Input Method" in Java

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package edu.xmu.guava.jcip;

import java.util.Map;

public interface Traversable {
	public void addWord(String word, int index);
	public Traversable getNext(Character c);
	public Map getChildren();
}

 

package edu.xmu.guava.jcip;

import java.util.Map;
import java.util.Scanner;
import java.util.Stack;
import java.util.TreeMap;

public class Dictionary {

	public static void main(String[] args) {

		Traversable rootNode = new VirtualHeaderNode();
		rootNode.addWord("Hello", 0);
		rootNode.addWord("Welcome", 0);
		rootNode.addWord("Yang", 0);
		rootNode.addWord("Yes", 0);
		rootNode.addWord("Good", 0);
		rootNode.addWord("God", 0);
		rootNode.addWord("Yeah", 0);
		rootNode.addWord("Yep", 0);

		System.out.println(rootNode.getChildren().keySet());

		Stack wordStack = new Stack();

		Scanner scanner = new Scanner(System.in);
		String str = scanner.next();
		Traversable currentNode = rootNode;
		wordStack.push(currentNode);
		while (true) {
			if ("POP".equals(str)) {
				if (!(wordStack.peek() instanceof VirtualHeaderNode)) {
					wordStack.pop();
					currentNode = wordStack.peek();
				}
			} else if ("EXIT".equals(str)) {
				scanner.close();
				break;
			} else {
				char alpha = str.charAt(0);
				if (currentNode.getChildren().containsKey(alpha)) {
					currentNode = currentNode.getChildren().get(alpha);
					wordStack.push(currentNode);
				}
			}
			Map next = currentNode
					.getChildren();
			System.out.println(next.keySet());
			str = scanner.next();
		};
	}

	public static class VirtualHeaderNode implements Traversable {
		private Map children = new TreeMap();
		@Override
		public void addWord(String word, int index) {
			char c = word.charAt(0);
			Traversable headerNode;
			if (children.containsKey(c)) {
				headerNode = children.get(c);
			} else {
				headerNode = new AlphabetNode();
				children.put(c, headerNode);
			}
			headerNode.addWord(word, index);
		}

		@Override
		public Traversable getNext(Character c) {
			return children.get(c);
		}

		@Override
		public Map getChildren() {
			return children;
		}

	}
	public static class AlphabetNode implements Traversable {
		private AlphabetNode parent;
		private Map children = new TreeMap();

		private char value;

		public void addWord(String word, int i) {
			this.value = word.charAt(i);

			if (i >= (word.length() - 1)) {
				return;
			}

			char childValue = word.charAt(i + 1);

			AlphabetNode childNode;
			if (children.containsKey(childValue)) {
				childNode = children.get(childValue);
			} else {
				childNode = new AlphabetNode();
				childNode.setParent(this);
				childNode.setValue(childValue);
				children.put(childValue, childNode);
			}
			childNode.addWord(word, i + 1);
		}
		public AlphabetNode getParent() {
			return parent;
		}

		public void setParent(AlphabetNode parent) {
			this.parent = parent;
		}

		public Map getChildren() {
			return children;
		}
		public void setChildren(Map children) {
			this.children = children;
		}
		public char getValue() {
			return value;
		}

		public void setValue(char value) {
			this.value = value;
		}

		@Override
		public String toString() {
			return "AlphabetNode [value=" + value + "]";
		}
		@Override
		public AlphabetNode getNext(Character c) {
			return children.get(c);
		}
	}

}