$ cat SerialComparator.java 
class SerialComparator implements java.util.Comparator,java.io.Serializable {
    public int compare(Object o1,Object o2) {
        return 7;
    }

    public boolean equals(Object o) {
        return true;
    }
}

$ /set/java/re/jdk/7/promoted/fcs/b147/binaries/solaris-sparc/bin/javac -g:none SerialComparator.java 

$ /set/java/re/jdk/7/promoted/fcs/b147/binaries/solaris-sparc/bin/serialver SerialComparator      
SerialComparator:    static final long serialVersionUID = 2879724379937955927L;

$ /set/java/re/jdk/8/promoted/ea/b81/binaries/solaris-sparc/bin/serialver SerialComparator
SerialComparator:    static final long serialVersionUID = 2879724379937955927L;

$ /set/java/re/jdk/8/promoted/ea/b82/binaries/solaris-sparc/bin/serialver SerialComparator
SerialComparator:    static final long serialVersionUID = -2781454083125382737L;