1    package classUtils.pack.util; 
2     
3    import java.io.*; 
4    import java.util.*; 
5     
6    public class PushbackReader extends FilterReader { 
7     
8        private ArrayList buf; 
9     
10       public PushbackReader(Reader r) { 
11           this(r,1); 
12       } 
13    
14       public PushbackReader(Reader r, int windowSize) { 
15           super(r); 
16           this.buf=new ArrayList(); 
17       } 
18    
19       public int read() throws IOException { 
20           int size=buf.size(); 
21           if (size==0) return super.read(); 
22           else { 
23               return ((Integer)buf.remove(buf.size()-1)).intValue(); 
24           } 
25       } 
26    
27       public void unread(int c) throws IOException { 
28           buf.add(new Integer(c)); 
29       } 
30    
31       private static void readAll(Reader r) throws IOException { 
32           int c; 
33           while((c=r.read())!=-1) System.out.print((char)c); 
34           System.out.println(); 
35       } 
36    
37       public static void main(String args[]) throws Exception { 
38           PushbackReader r = new PushbackReader(new StringReader("ciao")); 
39           readAll(r); 
40           r.unread('a'); 
41           r.unread('i'); 
42           r.unread('c'); 
43    
44           //r.unread('o'); 
45           readAll(r); 
46       } 
47   }