import java.util.*;

public class Context {

private StringTokenizer tokenizer;

private String currentToken;

public Context(String text) {

this.tokenizer = new StringTokenizer(text);

this.nextToken();

}

public String nextToken() {

if (this.tokenizer.hasMoreTokens()) {

this.currentToken = this.tokenizer.nextToken();

} else {

this.currentToken = null;

}

return this.currentToken;

}

public String currentToken() {

return this.currentToken;

}

public void skipToken(String token) throws ParseException {

if (! token.equals(this.currentToken)) {

throw new ParseException("Warning: try to skip `" + token + "` but found `" + this.currentToken);

}

this.nextToken();

}

public int currentNumber() throws ParseException {

int number = 0;

try {

number = Integer.parseInt(this.currentToken);

} catch (NumberFormatException e) {

throw new ParseException("Warning: " + e.toString());

}

return number;

}

}