boolean execute():
Executes the SQL statement in this Prepared Statement object, which may be any kind of SQL statement.
ResultSet executeQuery():
Executes the SQL query in this Prepared Statement object and returns the ResultSet object generated by the query.
int executeUpdate():
Executes the SQL statement in this Prepared Statement object, which must be an SQL INSERT, UPDATE or DELETE statement; or an SQL statement that returns nothing, such as a DDL statement.
The best place to find answers to questions like this is the Javadocs:
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