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Java > Open Source Codes > bsh > CommandLineReader


1 /*****************************************************************************
2  * *
3  * This file is part of the BeanShell Java Scripting distribution. *
4  * Documentation and updates may be found at http://www.beanshell.org/ *
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6  * Sun Public License Notice: *
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8  * The contents of this file are subject to the Sun Public License Version *
9  * 1.0 (the "License"); you may not use this file except in compliance with *
10  * the License. A copy of the License is available at http://www.sun.com *
11  * *
12  * The Original Code is BeanShell. The Initial Developer of the Original *
13  * Code is Pat Niemeyer. Portions created by Pat Niemeyer are Copyright *
14  * (C) 2000. All Rights Reserved. *
15  * *
16  * GNU Public License Notice: *
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18  * Alternatively, the contents of this file may be used under the terms of *
19  * the GNU Lesser General Public License (the "LGPL"), in which case the *
20  * provisions of LGPL are applicable instead of those above. If you wish to *
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27  * *
28  * Patrick Niemeyer (pat@pat.net) *
29  * Author of Learning Java, O'Reilly & Associates *
30  * http://www.pat.net/~pat/ *
31  * *
32  *****************************************************************************/
33
34
35 package bsh;
36
37 import java.io.*;
38
39 /**
40     This is a quick hack to turn empty lines entered interactively on the
41     command line into ';\n' empty lines for the interpreter. It's just more
42     pleasant to be able to hit return on an empty line and see the prompt
43     reappear.
44         
45     This is *not* used when text is sourced from a file non-interactively.
46 */
47 class CommandLineReader extends FilterReader {
48
49     public CommandLineReader( Reader in ) {
50         super(in);
51     }
52
53     static final int
54         normal = 0,
55         lastCharNL = 1,
56         sentSemi = 2;
57
58     int state = lastCharNL;
59
60     public int read() throws IOException {
61         int b;
62
63         if ( state == sentSemi ) {
64             state = lastCharNL;
65             return '\n';
66         }
67
68         // skip CR
69 while ( (b = in.read()) == '\r' );
70
71         if ( b == '\n' )
72             if ( state == lastCharNL ) {
73                 b = ';';
74                 state = sentSemi;
75             } else
76                 state = lastCharNL;
77         else
78             state = normal;
79
80         return b;
81     }
82
83     /**
84         This is a degenerate implementation.
85         I don't know how to keep this from blocking if we try to read more
86         than one char... There is no available() for Readers ??
87     */
88     public int read(char buff[], int off, int len) throws IOException
89     {
90         int b = read();
91         if ( b == -1 )
92             return -1; // EOF, not zero read apparently
93 else {
94             buff[off]=(char)b;
95             return 1;
96         }
97     }
98
99     // Test it
100 public static void main( String JavaDoc [] args ) throws Exception JavaDoc {
101         Reader in = new CommandLineReader( new InputStreamReader(System.in) );
102         while ( true )
103             System.out.println( in.read() );
104         
105     }
106 }
107
108
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