Mapping native and Java data types

Java and Genero have different primitive data types. Unlike Genero, Java is a strongly typed language: You cannot call a method with a String if it was defined to get an int parameter. To call a Java method, Genero native typed values need to be converted to/from Java types such as byte, int, short, char or data objects such as java.lang.String. If possible, the fglrun runtime system will do this conversion implicitly.

The fglcomp compiler will raise the error -6606, if the native data type does not match the Java (primitive) type, using Widening Primitive Conversions. For example, passing a Genero DECIMAL when a Java double is expected will fail, but passing a SMALLFLOAT (equivalent to float) when a Java double is expected will compile and run.

Genero has advanced native data types such as DECIMAL, which do not have an equivalent primitive type or class in Java. For such Genero types, you need to use a specific Java class provided in the $FGLDIR/lib/fgl.jar package, like com.fourjs.fgl.lang.FglDecimal. You can then manipulate the Genero specific value in the Java code.

Genero also implements structured types with RECORD definitions, converted to com.fourjs.fgl.lang.FglRecord objects for Java.

The Genero arrays cannot be used to call Java methods. You must use native Java arrays instead.

In some cases you need to explicitly cast with the new CAST() operator. See the topic about CAST() operator for more details.

The following tables show the implicit conversions done by the runtime system when a Java method is called, or when a Java method returns a value or object reference:

Table 1. Implicit BDL/Java conversions using simple types
Genero data type	Java equivalent
`BIGINT`	`long` (64-bit signed integer)
`BOOLEAN`	`Boolean`
`BYTE`	`com.fourjs.fgl.lang.FglByteBlob`
`CHAR`	`java.lang.String`
`DATE`	`com.fourjs.fgl.lang.FglDate`
`DATETIME`	`com.fourjs.fgl.lang.FglDateTime`
`DECIMAL`	`com.fourjs.fgl.lang.FglDecimal`
`FLOAT`	`double` (64-bit signed floating point number)
`INTEGER`	`int` (32-bit signed integer)
`INTERVAL`	`com.fourjs.fgl.lang.FglInterval`
`MONEY`	`com.fourjs.fgl.lang.FglDecimal`
`SMALLFLOAT`	`float` (32-bit signed floating point number)
`SMALLINT`	`short` (16-bit signed integer)
`STRING`	`java.lang.String`
`TEXT`	`com.fourjs.fgl.lang.FglTextBlob`
`TINYINT`	`byte` (8-bit signed integer)
`VARCHAR`	`java.lang.String`

Table 2. Implicit BDL/Java conversions using structured types
Genero data type	Java equivalent
`RECORD` structure	`com.fourjs.fgl.lang.FglRecord`
Java Array	This is a native Java Array

Table 3. Native BDL types that cannot be converted to Java types
Genero data type
ARRAY structures
Built-in classes