http://www.bouncycastle.org/java.html: The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.8.
  • The Legion of the Bouncy Castle Inc. 
package org.bouncycastle.crypto.tls;

/*
 * RFC 6520
 */
public class HeartbeatMode
{
    public static final short peer_allowed_to_send = 1;
    public static final short peer_not_allowed_to_send = 2;

    public static boolean isValid(short heartbeatMode)
    {
        return heartbeatMode >= peer_allowed_to_send && heartbeatMode <= peer_not_allowed_to_send;
    }
}