public static void main(String[] args) { analyze("I am happy about this"); analyze("I am not happy about this"); analyze("I am not! I am happy");...
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Smutek to uczucie, jak gdyby się tonęło, jak gdyby grzebano cię w ziemi.
hasMoreTokens()) {
String token = next();
// Look until you find one of the
// two starting tokens:
if(!token.equals("I") &&
!token.equals("Are"))
continue; // Top of while loop
if(token.equals("I")) {
String tk2 = next();
if(!tk2.equals("am")) // Must be after I
break; // Out of while loop
Chapter 10: The Java IO System
381
else {
String tk3 = next();
if(tk3.equals("sad")) {
sad = true;
break; // Out of while loop
}
if (tk3.equals("not")) {
String tk4 = next();
if(tk4.equals("sad"))
break; // Leave sad false
if(tk4.equals("happy")) {
sad = true;
break;
}
}
}
}
if(token.equals("Are")) {
String tk2 = next();
if(!tk2.equals("you"))
break; // Must be after Are
String tk3 = next();
if(tk3.equals("sad"))
sad = true;
break; // Out of while loop
}
}
if(sad) prt("Sad detected");
}
static String next() {
if(st.hasMoreTokens()) {
String s = st.nextToken();
prt(s);
return s;
}
else
return "";
}
static void prt(String s) {
System.out.println(s);
}
} ///:~
For each string being analyzed, a while loop is entered and tokens are pulled off the string.
Notice the first if statement, which says to continue (go back to the beginning of the loop and start again) if the token is neither an “I” nor an “Are.” This means that it will get tokens until an “I” or an “Are” is found. You might think to use the == instead of the equals( ) method, but that won’t work correctly, since == compares handle values while equals( ) compares contents.
The logic of the rest of the analyze( ) method is that the pattern that’s being searched for is
“I am sad,” “I am not happy,” or “Are you sad?” Without the break statement, the code for this would be even messier than it is. You should be aware that a typical parser (this is a 382
Thinking in Java
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primitive example of one) normally has a table of these tokens and a piece of code that moves through the states in the table as new tokens are read.
You should think of the StringTokenizer only as shorthand for a simple and specific kind of StreamTokenizer. However, if you have a String that you want to tokenize and StringTokenizer is too limited, all you have to do is turn it into a stream with StringBufferInputStream and then use that to create a much more powerful StreamTokenizer.
Java 1.1 IO streams
At this point you might be scratching your head, wondering if there is another design for IO
streams that could require more typing. Could someone have come up with an odder design?” Prepare yourself: Java 1.1 makes some significant modifications to the IO stream library. When you see the Reader and Writer classes your first thought (like mine) might be that these were meant to replace the InputStream and OutputStream classes. But that’s not the case. Although some aspects of the original streams library are deprecated (if you use them you will receive a warning from the compiler), the old streams have been left in for backwards compatibility and:
1. New classes have been put into the old hierarchy, so it’s obvious that Sun is not abandoning the old streams.
2. There are times when you’re supposed to use classes in the old hierarchy in combination with classes in the new hierarchy and to accomplish this there are “bridge” classes: InputStreamReader converts an InputStream to a Reader and OutputStreamWriter converts an OutputStream to a Writer.
As a result there are situations in which you have more layers of wrapping with the new IO
stream library than with the old. Again, this is a drawback of the decorator pattern – the price you pay for added flexibility.
The most important reason for adding the Reader and Writer hierarchies in Java 1.1 is for internationalization. The old IO stream hierarchy supports only 8-bit byte streams and doesn’t handle the 16-bit Unicode characters well. Since Unicode is used for
internationalization (and Java’s native char is 16-bit Unicode), the Reader and Writer hierarchies were added to support Unicode in all IO operations. In addition, the new libraries are designed for faster operations than the old.