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annotate src/goodjava/io/BufferedInputStream.java @ 1493:471ef3e6a84e

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author Franklin Schmidt <fschmidt@gmail.com>
date Sun, 03 May 2020 00:12:15 -0600
parents fe237d72b234
children 91c167099462
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1 /*
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2 * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
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3 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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4 */
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5
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6 package goodjava.io;
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7
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8 import java.io.InputStream;
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9 import java.io.FilterInputStream;
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10 import java.io.IOException;
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11
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12 /**
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13 * A <code>BufferedInputStream</code> adds
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14 * functionality to another input stream-namely,
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15 * the ability to buffer the input. When the <code>BufferedInputStream</code>
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16 * is created, an internal buffer array is
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17 * created. As bytes from the stream are read
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18 * or skipped, the internal buffer is refilled
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19 * as necessary from the contained input stream,
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20 * many bytes at a time.
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21 *
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22 * @author Arthur van Hoff
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23 * @since JDK1.0
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24 */
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25 public final class BufferedInputStream extends FilterInputStream {
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26 private final byte buf[];
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27
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28 /**
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29 * The index one greater than the index of the last valid byte in
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30 * the buffer.
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31 * This value is always
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32 * in the range <code>0</code> through <code>buf.length</code>;
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33 * elements <code>buf[0]</code> through <code>buf[count-1]
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34 * </code>contain buffered input data obtained
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35 * from the underlying input stream.
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36 */
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37 private int count;
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38
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39 /**
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40 * The current position in the buffer. This is the index of the next
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41 * character to be read from the <code>buf</code> array.
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42 * <p>
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43 * This value is always in the range <code>0</code>
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44 * through <code>count</code>. If it is less
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45 * than <code>count</code>, then <code>buf[pos]</code>
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46 * is the next byte to be supplied as input;
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47 * if it is equal to <code>count</code>, then
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48 * the next <code>read</code> or <code>skip</code>
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49 * operation will require more bytes to be
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50 * read from the contained input stream.
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51 *
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52 * @see java.io.BufferedInputStream#buf
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53 */
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54 private int pos;
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55
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56 /**
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57 * Creates a <code>BufferedInputStream</code>
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58 * and saves its argument, the input stream
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59 * <code>in</code>, for later use. An internal
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60 * buffer array is created and stored in <code>buf</code>.
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61 *
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62 * @param in the underlying input stream.
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63 */
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64 public BufferedInputStream(InputStream in) {
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65 this(in, 8192);
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66 }
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67
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68 /**
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69 * Creates a <code>BufferedInputStream</code>
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70 * with the specified buffer size,
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71 * and saves its argument, the input stream
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72 * <code>in</code>, for later use. An internal
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73 * buffer array of length <code>size</code>
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74 * is created and stored in <code>buf</code>.
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75 *
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76 * @param in the underlying input stream.
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77 * @param size the buffer size.
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78 */
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79 public BufferedInputStream(InputStream in, int size) {
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80 super(in);
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81 buf = new byte[size];
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82 }
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83
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84 /**
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85 * Fills the buffer with more data.
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86 * Assumes that it is being called by a synchronized method.
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87 * This method also assumes that all data has already been read in,
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88 * hence pos > count.
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89 */
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90 private void fill() throws IOException {
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91 pos = 0;
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92 count = 0;
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93 int n = super.read(buf, 0, buf.length);
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94 if (n > 0)
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95 count = n;
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96 }
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97
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98 /**
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99 * See
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100 * the general contract of the <code>read</code>
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101 * method of <code>InputStream</code>.
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102 *
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103 * @return the next byte of data, or <code>-1</code> if the end of the
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104 * stream is reached.
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105 * @exception IOException if this input stream has been closed by
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106 * invoking its {@link #close()} method,
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107 * or an I/O error occurs.
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108 * @see java.io.FilterInputStream#in
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109 */
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110 public synchronized int read() throws IOException {
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111 if (pos >= count) {
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112 fill();
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113 if (pos >= count)
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114 return -1;
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115 }
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116 return buf[pos++] & 0xff;
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117 }
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118
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119 /**
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120 * Read characters into a portion of an array, reading from the underlying
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121 * stream at most once if necessary.
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122 */
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123 private int read1(byte[] b, int off, int len) throws IOException {
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124 int cnt = 0;
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125 int avail = count - pos;
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126 if( avail > 0 ) {
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127 cnt = (avail < len) ? avail : len;
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128 System.arraycopy(buf, pos, b, off, cnt);
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129 pos += cnt;
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130 len -= cnt;
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131 if( len == 0 )
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132 return cnt;
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133 off += cnt;
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134 }
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135 if (len >= buf.length) {
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136 return cnt + Math.max( 0, super.read(b, off, len) );
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137 }
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138 fill();
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139 if (count <= 0)
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140 return cnt;
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141 System.arraycopy(buf, 0, b, off, len);
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142 pos += len;
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143 return cnt + len;
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144 }
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145
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146 public synchronized int read(byte[] b, int off, int len) throws IOException {
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147 if( len == 0 )
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148 return 0;
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149 int n = read1(b,off,len);
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150 return n==0 ? -1 : n;
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151 }
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152
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153 /**
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154 * See the general contract of the <code>skip</code>
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155 * method of <code>InputStream</code>.
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156 *
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157 * @exception IOException if the stream does not support seek,
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158 * or if this input stream has been closed by
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159 * invoking its {@link #close()} method, or an
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160 * I/O error occurs.
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161 */
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162 public synchronized long skip(long n) throws IOException {
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163 if( n <= 0 )
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164 return 0;
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165 long skipped = 0;
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166 long avail = count - pos;
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167 if( avail > 0 ) {
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168 skipped = (avail < n) ? avail : n;
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169 pos += skipped;
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170 n -= skipped;
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171 if( n == 0 )
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172 return skipped;
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173 }
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174 return skipped + super.skip(n);
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175 }
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176
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177 /**
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178 * Returns an estimate of the number of bytes that can be read (or
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179 * skipped over) from this input stream without blocking by the next
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180 * invocation of a method for this input stream. The next invocation might be
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181 * the same thread or another thread. A single read or skip of this
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182 * many bytes will not block, but may read or skip fewer bytes.
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183 * <p>
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184 * This method returns the sum of the number of bytes remaining to be read in
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185 * the buffer (<code>count&nbsp;- pos</code>) and the result of calling the
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186 * {@link java.io.FilterInputStream#in in}.available().
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187 *
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188 * @return an estimate of the number of bytes that can be read (or skipped
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189 * over) from this input stream without blocking.
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190 * @exception IOException if this input stream has been closed by
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191 * invoking its {@link #close()} method,
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192 * or an I/O error occurs.
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193 */
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194 public synchronized int available() throws IOException {
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195 int n = count - pos;
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196 int avail = super.available();
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197 return n > (Integer.MAX_VALUE - avail)
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198 ? Integer.MAX_VALUE
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199 : n + avail;
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200 }
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201
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202 public void mark(int readlimit) {}
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203
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204 public void reset() throws IOException {
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205 throw new IOException("mark/reset not supported");
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206 }
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207
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208 public boolean markSupported() {
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209 return false;
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210 }
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211
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212 }