https://openjdk.java.net/ 
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package com.sun.security.auth;


An object that implements the java.security.Principal
interface typically also implements this interface to provide
a means for comparing that object to a specified Subject.

 The comparison is achieved via the implies method.
The implementation of the implies method determines
whether this object "implies" the specified Subject.
One example application of this method may be for
a "group" object to imply a particular Subject
if that Subject belongs to the group.
Another example application of this method would be for
"role" object to imply a particular Subject
if that Subject is currently acting in that role.

 Although classes that implement this interface typically
also implement the java.security.Principal interface,
it is not required.  In other words, classes may implement the
java.security.Principal interface by itself,
the PrincipalComparator interface by itself,
or both at the same time.

See Also:
/**
 * An object that implements the <code>java.security.Principal</code>
 * interface typically also implements this interface to provide
 * a means for comparing that object to a specified <code>Subject</code>.
 *
 * <p> The comparison is achieved via the <code>implies</code> method.
 * The implementation of the <code>implies</code> method determines
 * whether this object "implies" the specified <code>Subject</code>.
 * One example application of this method may be for
 * a "group" object to imply a particular <code>Subject</code>
 * if that <code>Subject</code> belongs to the group.
 * Another example application of this method would be for
 * "role" object to imply a particular <code>Subject</code>
 * if that <code>Subject</code> is currently acting in that role.
 *
 * <p> Although classes that implement this interface typically
 * also implement the <code>java.security.Principal</code> interface,
 * it is not required.  In other words, classes may implement the
 * <code>java.security.Principal</code> interface by itself,
 * the <code>PrincipalComparator</code> interface by itself,
 * or both at the same time.
 *
 * @see java.security.Principal
 * @see javax.security.auth.Subject
 */
@jdk.Exported
public interface PrincipalComparator {
    
Check if the specified Subject is implied by
this object.



Returns:true if the specified Subject is implied by
         this object, or false otherwise.
/**
     * Check if the specified <code>Subject</code> is implied by
     * this object.
     *
     * <p>
     *
     * @return true if the specified <code>Subject</code> is implied by
     *          this object, or false otherwise.
     */
    boolean implies(javax.security.auth.Subject subject);
}