The Java Developers Almanac 1.4

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e159. Getting Bytes from a ByteBuffer

A ByteBuffer has a capacity that determines how many bytes it contains. This capacity can never change. Any byte in the buffer can be retrieved using the absolute version of get(), which takes an index in the range [0..capacity-1].

The bytes in a ByteBuffer can also be retrieved using the relative version of get(), which uses the position and limit properties of the buffer. In particular, this version of get() retrieves the byte at the position and advances the position by one. get() cannot retrieve bytes past the limit (even though the limit might be less than the capacity). The position is always <= limit and limit is always <= capacity.

    // Create an empty ByteBuffer with a 10 byte capacity
    ByteBuffer bbuf = ByteBuffer.allocate(10);
    
    // Get the ByteBuffer's capacity
    int capacity = bbuf.capacity(); // 10
    
    // Use the absolute get().
    // This method does not affect the position.
    byte b = bbuf.get(5); // position=0
    
    // Set the position
    bbuf.position(5);
    
    // Use the relative get()
    b = bbuf.get();
    
    // Get the new position
    int pos = bbuf.position(); // 6
    
    // Get remaining byte count
    int rem = bbuf.remaining(); // 4
    
    // Set the limit
    bbuf.limit(7); // remaining=1
    
    // This convenience method sets the position to 0
    bbuf.rewind(); // remaining=7