InputStream

package java.io;

public abstract class InputStream implements Closeable {
    
    private static final int MAX_SKIP_BUFFER_SIZE = 2048;
    
    public abstract int read() throws IOException;
    
    public int read(byte[] b) throws IOException {
        return read(b, 0, b.length);
    }
    
    public int read(byte[] b, int off, int len) throws IOException {
        if (b == null) {
            throw new NullPointerException();
        } else if (off < 0 || len < 0 || len > b.length - off) {
            throw new IndexOutOfBoundsException();
        } else if (len ==0) {
            return 0;
        }
        
        int c = read();
        
        if (c == -1) {
            return -1;
        }
        b[off] = (byte)c;
        
        int i = 1;
        try {
            for (; i < len; i++) {
                c = read();
                if (c == -1) {
                    break;
                }
                b[off + i] = (byte)c;
            }
        } catch (IOException ee) {
        }
        
        return i;
    }
    
    public long skip(long n) throws IOException {
        long remaining = n;
        int nr;
        
        if (n <= 0) {
            return 0;
        }
        
        int size = (int)Math.min(MAX_SKIP_BUFFER_SIZE, remaining);
        byte[] skipBuffer = new byte[size];
        while (remaining > 0) {
            nr = read(skipBuffer, 0, (int)Math.min(size, remaining));
            if (nr < 0) {
                break;
            }
            remaining -= nr;
        }
        return n - remaining;    
    } 
    
    public int available() throws IOException {
        return 0;
    }
    
    public void close() throws IOException {}
    
    public synchronized void mark(int readlimit) {}
    
    public synchronized void reset() throws IOException {
        throw new IOException("mark/reset not supported");
    }
    
    public boolean markSupported() {
        return false;
    }
    
}

 read()方法阻塞的情况：

执行上述代码，在控制台输入数据之前程序将一直阻塞在read方法