Find Definition of a abstract class in Java

i have an interface which has an abstract method

public abstract String newId(Connection paramConnection, String paramString1, long paramLong1, long paramLong2, long paramLong3, String paramString2, Map paramMap, int paramInt)
throws IOException;

in a JAR.

But how do i find where exactly in the Run time we define this method/override this method to get Retun string value .?