List the main data types used in JDBC and explain how they relate to data types in Java.

The main JDBC data types are defined in the java.sql.Types class. They represent standard SQL types. JVM data types in Java are defined in the language specification. JDBC provides a mapping between these two sets of types.

Main types in java.sql.Types:

• BOOLEAN
• TINYINT
• SMALLINT
• INTEGER
• BIGINT
• REAL
• FLOAT
• DOUBLE
• DECIMAL
• NUMERIC
• CHAR
• VARCHAR
• LONGVARCHAR
• DATE
• TIME
• TIMESTAMP
• BINARY
• VARBINARY
• LONGVARBINARY
• BLOB
• CLOB
• NCHAR
• NVARCHAR
• LONGNVARCHAR
• NCLOB
• SQLXML

Mapping between JDBC types and Java types when retrieving data (from ResultSet):

JDBC Type	Java Type (get)	Notes
BOOLEAN, BIT	boolean
TINYINT	byte
SMALLINT	short
INTEGER	int
BIGINT	long
REAL	float
FLOAT, DOUBLE	double
DECIMAL, NUMERIC	java.math.BigDecimal	Recommended
CHAR, VARCHAR, LONGVARCHAR	String
DATE	java.sql.Date
TIME	java.sql.Time
TIMESTAMP	java.sql.Timestamp
BINARY, VARBINARY, LONGVARBINARY	byte[]
BLOB	java.sql.Blob
CLOB	java.sql.Clob
NCHAR, NVARCHAR, LONGNVARCHAR	String
NCLOB	java.sql.NClob
SQLXML	java.sql.SQLXML

Note: For numeric types, besides primitive types, you can use corresponding wrapper classes (Boolean, Byte, Short, Integer, Long, Float, Double) to handle NULL values.

When setting data (in PreparedStatement), the typical mapping is reversed, but there are exceptions and preferences. For example, for DECIMAL, it is better to use BigDecimal.

Example usage:

// Method to get data from ResultSet
public String getStringValue(ResultSet rs, String columnName) throws SQLException {
    // Get string value from column
    return rs.getString(columnName);
}

// Method to set parameter in PreparedStatement
public void setIntValue(PreparedStatement ps, int parameterIndex, int value) throws SQLException {
    // Set integer value in query parameter
    ps.setInt(parameterIndex, value);
}