1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208

package Torello.Java.Additional;

import Torello.JavaDoc.JDHeaderBackgroundImg;
import Torello.Java.UnreachableError;

// Used for the JavaDoc '@see' tag, a few lines directly-below
import Torello.Java.OSCommands;

import java.io.IOException;

/**
 * Builds a composite {@code java.lang.Appendable} using up to <B STYLE='color: red;'>three</B>
 * independent input-parameter {@code Appendable's}.  Character data appended to an instance of
 * {@code TriAppendable} will, in turn, be appended to any of the input-{@code Appendable's} which
 * have been provided to this class' constructor and are non-null.
 * 
 * <BR /><BR />Passing null input-{@code Appendable's} <B STYLE='color: red;'><I>will not</I></B>
 * cause this class to fail, and <B STYLE='color: red;'><I>will not</I></B> generate
 * {@code NullPointerException's}.  One of the primary values of this class is that the chunk of
 * code that tests for a "Null Log" is done inside this class.
 * 
 * <BR /><BR />The meaning of a "Null Log" is just that a user has decided against logging a tool 
 * or utility's output to any logger, and has passed 'null' to one of the log references in his
 * code.
 * 
 * @see OSCommands
 */
@JDHeaderBackgroundImg
    (EmbedTagFileID={"APPENDABLE_EXTENSION", "TRI_APPENDABLE_JDHBI", "BI_TRI_BOTH_JDHBI"})
public class TriAppendable implements Appendable
{
    private final Appendable appendable;

    /**
     * Creates an instance of this class, using up to three input {@code Appendable's}.
     * 
     * @param a Any {@code java.lang.Appendable}.  This parameter may be null, and if it is it will
     * be ignored.  Passing null here, will not generated a {@code NullPointerException}
     * 
     * @param b Any {@code java.lang.Appendable}.  This parameter may be null, and if it is it will
     * be ignored.  Passing null here, will not generated a {@code NullPointerException}
     * 
     * @param c Any {@code java.lang.Appendable}.  This parameter may be null, and if it is it will
     * be ignored.  Passing null here, will not generated a {@code NullPointerException}
     */
    public TriAppendable(Appendable a, Appendable b, Appendable c)
    {
        // Minor coding trick.  Pretend this is a base-2 number, with three bits.  I think this
        // improves efficiency a tiny bit, since it isn't comparing the nulls over and over again.
        // Here it checks the references for nulls only once.

        int theSum =
            ((a == null) ? 0 : 4) +
            ((b == null) ? 0 : 2) +
            ((c == null) ? 0 : 1);
        
        // if ((a == null) && (b == null) && (c == null)) this.appendable = new Appendable()
        if (theSum == 0) this.appendable = new Appendable()
        {
            public Appendable append(char ch) throws IOException
            { return this; }
    
            public Appendable append(CharSequence cs) throws IOException
            { return this; }

            public Appendable append(CharSequence cs, int start, int end) throws IOException
            { return this; }
        };

        // else if ((a == null) && (b == null) && (c != null)) this.appendable = new Appendable()
        else if (theSum == 1) this.appendable = new Appendable()
        {
            public Appendable append(char ch) throws IOException
            { c.append(ch); return this; }
    
            public Appendable append(CharSequence cs) throws IOException
            { c.append(cs); return this; }

            public Appendable append(CharSequence cs, int start, int end) throws IOException
            { c.append(cs, start, end); return this; }
        };

        // else if ((a == null) && (b != null) && (c == null)) this.appendable = new Appendable()
        else if (theSum == 2) this.appendable = new Appendable()
        {
            public Appendable append(char ch) throws IOException
            { b.append(ch); return this; }
    
            public Appendable append(CharSequence cs) throws IOException
            { b.append(cs); return this; }

            public Appendable append(CharSequence cs, int start, int end) throws IOException
            { b.append(cs, start, end); return this; }
        };

        // else if ((a == null) && (b != null) && (c != null)) this.appendable = new Appendable()
        else if (theSum == 3) this.appendable = new Appendable()
        {
            public Appendable append(char ch) throws IOException
            { b.append(ch); c.append(ch); return this; }
    
            public Appendable append(CharSequence cs) throws IOException
            { b.append(cs); c.append(cs); return this; }

            public Appendable append(CharSequence cs, int start, int end) throws IOException
            { b.append(cs, start, end); c.append(cs, start, end); return this; }
        };

        // else if ((a != null) && (b == null) && (c == null)) this.appendable = new Appendable()
        else if (theSum == 4) this.appendable = new Appendable()
        {
            public Appendable append(char ch) throws IOException
            { a.append(ch); return this; }
    
            public Appendable append(CharSequence cs) throws IOException
            { a.append(cs); return this; }

            public Appendable append(CharSequence cs, int start, int end) throws IOException
            { a.append(cs, start, end); return this; }
        };

        // else if ((a != null) && (b == null) && (c != null)) this.appendable = new Appendable()
        else if (theSum == 5) this.appendable = new Appendable()
        {
            public Appendable append(char ch) throws IOException
            { a.append(ch); c.append(ch); return this; }
    
            public Appendable append(CharSequence cs) throws IOException
            { a.append(cs); c.append(cs); return this; }

            public Appendable append(CharSequence cs, int start, int end) throws IOException
            { a.append(cs, start, end); c.append(cs, start, end); return this; }
        };

        // else if ((a != null) && (b != null) && (c == null)) this.appendable = new Appendable()
        else if (theSum == 6) this.appendable = new Appendable()
        {
            public Appendable append(char ch) throws IOException
            { a.append(ch); b.append(ch); return this; }
    
            public Appendable append(CharSequence cs) throws IOException
            { a.append(cs); b.append(cs); return this; }

            public Appendable append(CharSequence cs, int start, int end) throws IOException
            { a.append(cs, start, end); b.append(cs, start, end); return this; }
        };

        // else if ((a != null) && (b != null) && (c != null)) this.appendable = new Appendable()
        else if (theSum == 7) this.appendable = new Appendable()
        {
            public Appendable append(char ch) throws IOException
            { a.append(ch); b.append(ch); c.append(ch); return this; }
    
            public Appendable append(CharSequence cs) throws IOException
            { a.append(cs); b.append(cs); c.append(cs); return this; }

            public Appendable append(CharSequence cs, int start, int end) throws IOException
            { a.append(cs, start, end); b.append(cs, start, end); c.append(cs, start, end); return this; }
        };

        // This appears (on cursory inspection) very "unreachable".  However the java compiler
        // doesn't seem to like it!  (javac complains without this last line)

        else throw new UnreachableError();
    }

    /**
     * Logs a {@code char} (input-parameter {@code 'ch'}) to any / all non-null
     * {@code Appendable's} that were passed to this class' constructor.
     * 
     * @param ch Any Java Character
     * 
     * @throws IOException Throws if any of the underlying {@code Appendable's} throw
     * {@code IOException} upon having their corresponding {@code append()}-method invoked.
     */
    public Appendable append(char ch) throws IOException
    { return this.appendable.append(ch); }

    /**
     * Logs a {@code CharSequence} (input-parameter {@code 'cs'}) to any / all non-null
     * {@code Appendable's} that were passed to this class' constructor.
     * 
     * @param cs Any Java {@code CharSequence}
     * 
     * @throws IOException Throws if any of the underlying {@code Appendable's} throw
     * {@code IOException} upon having their corresponding {@code append()}-method invoked.
     */
    public Appendable append(CharSequence cs) throws IOException
    { return this.appendable.append(cs); }

    /**
     * Logs a partial / substring {@code CharSequence} (input-parameter {@code 'cs'}) to any / all
     * non-null {@code Appendable's} that were passed to this class' constructor.
     * 
     * @param cs Any Java {@code CharSequence}
     * 
     * @param start Position within {@code 'cs'} of the {@code substring's} first character to be
     * appended
     * 
     * @param end Position within {@code 'cs'} of the {@code substring's} last character to be
     * appended
     * 
     * @throws IOException Throws if any of the underlying {@code Appendable's} throw
     * {@code IOException} upon having their corresponding {@code append()}-method invoked.
     */
    public Appendable append(CharSequence cs, int start, int end) throws IOException
    { return this.appendable.append(cs, start, end); }
}