/**
 * A class to represent the elements of the language (tokens): integer and symbols.
 * 
 * @author Marcel Turcotte
 */

class Token {

    // constants

    private static final int INTEGER = 1;
    private static final int SYMBOL = 2;

    // instance variables

    private int iValue;
    private String sValue;

    private int type;

    /**
     * Creates a token that represents an integer value.
     */

    Token( int iValue ) {
        this.iValue = iValue;
        type = INTEGER;
    }

    /**
     * Creates a token that represents a symbol.
     */

    Token( String sValue ) {
        this.sValue = sValue;
        type = SYMBOL;
    }

    /**
     * Returns the integer value that is stored in this token; this
     * method is only applicable if this token isInteger.
     *
     * @return The int value stored in this token.
     */

    public int iValue() {

        // pre-condition

        if (type != INTEGER)
            throw new IllegalStateException("not an integer");

        return iValue;
    }

    /**
     * Returns the symbol (a String) that is stored in this token;
     * this method is only applicable if this token isSymbol.
     *
     * @return The symbol stored in this token.
     */

    public String sValue() {

        // pre-condition

        if (type != SYMBOL)
            throw new IllegalStateException("not a symbol");

        return sValue;
    }

    /**
     * Returns true if this token represents an integer value.
     *
     * @return true if this token is a integer.
     */

    public boolean isInteger() {
        return type == INTEGER;
    }

    /**
     * Returns true if this token represents a symbol.
     *
     * @return true if this token is a symbol.
     */

    public boolean isSymbol() {
        return type == SYMBOL;
    }

    /**
     * Returns a String representation of this token.
     *
     * @return A String representation of this token.
     */

    public String toString() {
        String result;

        switch (type) {
        case INTEGER:
            return Integer.toString(iValue);
        case SYMBOL:
            return sValue;
        default:
            throw new IllegalStateException("this statement should never be executed");
        }
    }
}