flesh out serialization/deserialization code and fix build

classpath/java/io/PushbackReader.java

@@ -0,0 +1,69 @@
+package java.io;
+
+public class PushbackReader extends Reader {
+  private final Reader in;
+  private final char[] buffer;
+  private int position;
+  private int limit;
+
+  public PushbackReader(Reader in, int bufferSize) {
+    this.in = in;
+    this.buffer = new char[bufferSize];
+  }
+
+  public PushbackReader(Reader in) {
+    this(in, 1);
+  }
+
+  public int read(char[] b, int offset, int length) throws IOException {
+    int count = 0;
+
+    if (position < limit) {
+      int remaining = limit - position;
+      if (remaining > length) {
+        remaining = length;
+      }
+
+      System.arraycopy(buffer, position, b, offset, remaining);
+
+      count += remaining;
+      position += remaining;
+      offset += remaining;
+      length -= remaining;
+    }
+
+    if (length > 0) {
+      int c = in.read(b, offset, length);
+      if (c == -1) {
+        if (count == 0) {
+          count = -1;
+        }
+      } else {
+        count += c;
+      }
+    }
+
+    return count;
+  }
+
+  public void unread(char[] b, int offset, int length) throws IOException {
+    if (position < length) {
+      throw new IOException(length + " not in [0," + position + "]");
+    } else {
+      System.arraycopy(buffer, position - length, b, offset, length);
+      position -= length;
+    }
+  }
+
+  public void unread(char[] b) throws IOException {
+    unread(b, 0, b.length);
+  }
+
+  public void unread(int c) throws IOException {
+    unread(new char[] { (char) c });
+  }
+
+  public void close() throws IOException {
+    in.close();
+  }
+}