Class Lexer

java.lang.Object
  Lexer

public class Lexer

extends java.lang.Object

This class is aimed at lexical analysis of a string representing an expression that may contain unsigned integers, variable names, operators, parentheses and whitespaces.

Field Summary

static int	TT_END A token type that identifies the end of input string.
static int	TT_LEFT_PAR A token type that identifies the left parenthesis.
static int	TT_NUMBER A token type that identifies a number.
static int	TT_OPERATOR A token type that identifies an operator ('+', '-' or '*').
static int	TT_RIGHT_PAR A token type that identifies the right parenthesis.
static int	TT_UNKNOWN Unknown token.
static int	TT_VAR A token type that identifies a variable.

Constructor Summary

Lexer(java.lang.String str)
Creates a lexer.

Method Summary

int	currentPosition() Returns the curent position in the string scanned.
int	nextToken() Returns the type of the next token.
int	number() Returns the integer representing a number if the last call of nextToken() returned TT_NUMBER.
char	operator() Returns the character representing an operator if the last call of nextToken() returned TT_OPERATOR.
java.lang.String	var() Returns the string representing a variable if the last call of nextToken() returned TT_VAR.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

TT_END

public static final int TT_END

A token type that identifies the end of input string.

See Also:

Constant Field Values

TT_UNKNOWN

public static final int TT_UNKNOWN

Unknown token.

See Also:

Constant Field Values

TT_NUMBER

public static final int TT_NUMBER

A token type that identifies a number.

See Also:

Constant Field Values

TT_VAR

public static final int TT_VAR

A token type that identifies a variable.

See Also:

Constant Field Values

TT_OPERATOR

public static final int TT_OPERATOR

A token type that identifies an operator ('+', '-' or '*').

See Also:

Constant Field Values

TT_LEFT_PAR

public static final int TT_LEFT_PAR

A token type that identifies the left parenthesis.

See Also:

Constant Field Values

TT_RIGHT_PAR

public static final int TT_RIGHT_PAR

A token type that identifies the right parenthesis.

See Also:

Constant Field Values

Constructor Detail

Lexer

public Lexer(java.lang.String str)

Creates a lexer.

Parameters:

str - a string representing an expression to be scanned

Throws:

java.lang.NullPointerException - if the parameter str is null

Method Detail

nextToken

public int nextToken()

Returns the type of the next token.

var

public java.lang.String var()

Returns the string representing a variable if the last call of nextToken() returned TT_VAR.

Throws:

java.lang.IllegalStateException - if the last call of nextToken() did not return TT_VAR

See Also:

nextToken()

number

public int number()

Returns the integer representing a number if the last call of nextToken() returned TT_NUMBER.

Throws:

java.lang.IllegalStateException - if the last call of nextToken() did not return TT_NUMBER

See Also:

nextToken()

operator

public char operator()

Returns the character representing an operator if the last call of nextToken() returned TT_OPERATOR.

Throws:

java.lang.IllegalStateException - if the last call of nextToken() did not return TT_OPERATOR

See Also:

nextToken()

currentPosition

public int currentPosition()

Returns the curent position in the string scanned.