Input and Output - Java - page 375

}

}

The StreamTokenizer class in java.util provides slightly more capabilities for scanning a
file. It reads characters and assembles them into words, or tokens. It returns these tokens to
you along with a type code describing the kind of token it found. This type code is one of
four predefined types ( StringTokenizer.TT_WORD , TT_NUMBER , TT_EOF , or TT_EOL for the
end-of-line), or the char value of an ordinary character (such as 32 for the space character).
Methods such as ordinaryCharacter() allow you to specify how to categorize characters,
while others such as slashSlashComment() allow you to enable or disable features.

Example 10-4 shows a StreamTokenizer used to implement a simple immediate-mode
stack-based calculator:

2 2 + =
4
22 7 / =
3.141592857

I read tokens as they arrive from the StreamTokenizer . Numbers are put on the stack. The
four operators ( + , - , \* , and / ) are immediately performed on the two elements at the top of
the stack, and the result is put back on the top of the stack. The = operator causes the top ele-
ment to be printed, but is left on the stack so that you can say:

4 5 * = 2 / =
20.0
10.0

Example 10-4. Simple calculator using StreamTokenizer
public public class SimpleCalcStreamTok {

/** The StreamTokenizer Input */
protected

class SimpleCalcStreamTok

protected StreamTokenizer tf ;
/** The Output File */
protected

protected PrintWriter out = new new PrintWriter ( System . out , true true );

/** The variable name (not used in this version) */
protected

protected String variable ;
/** The operand stack */
protected protected Stack s ;