5.1.2 Executing Statements Using Statement Objects

The Statement interface provides three different methods for executing SQL statements: executeQuery, executeUpdate, and execute. The correct method to use is determined by what the SQL statement produces.
The method executeQuery is designed for statements that produce a single result set, such as SELECT statements.
The method executeUpdate is used to execute INSERT, UPDATE, or DELETE statements and also SQL DDL (Data Definition Language) statements like CREATE TABLE, DROP TABLE, and ALTER TABLE. The effect of an INSERT, UPDATE, or DELETE statement is a modification of one or more columns in zero or more rows in a table. The return value of executeUpdate is an integer (referred to as the update count) that indicates the number of rows that were affected. For statements such as CREATE TABLE or DROP TABLE, which do not operate on rows, the return value of executeUpdate is always zero.

The method execute is used to execute statements that return more than one result set, more than one update count, or a combination of the two. Because it is an advanced feature that the majority of programmers will never use, it is explained in its own section later in this overview.
The Statement methods executeQuery and executeUpdate close the calling Statement object's current result set if there is one open. This means that any processing of the current ResultSet object needs to be completed before a Statement object is re-executed.
It should be noted that the PreparedStatement interface, which inherits all of the methods in the Statement interface, has its own versions of the methods executeQuery, executeUpdate and execute. Statement objects do not themselves contain an SQL statement; therefore, one must be provided as the argument to the Statement.execute methods. PreparedStatement objects do not supply an SQL statement as a parameter to these methods because they already contain a precompiled SQL statement. CallableStatement objects, which call one of the DBMS's stored procedures, inherit the PreparedStatement forms of these methods. Supplying an SQL statement to the PreparedStatement or CallableStatement versions of the methods executeQuery, executeUpdate, or execute will cause an SQLException to be thrown.