Using Java arrays

Java arrays and Genero arrays are different. In order to interface with Java arrays, the Genero language has been extended with a new kind of array, called "Java arrays".

Java arrays have to be created with a given length. Like native Java arrays, the length cannot be changed after the array is created.

In BDL Java arrays, the first element of is at index position 1, while in Java code, the first element of an array starts at index 0 (zero).

To create a Java array in Genero, you must define a TYPE in order to call the create() type method of Java arrays. The type of the elements in a Java array must be one of the language types that have a corresponding primitive type in Java (such as INTEGER (int), FLOAT (double)), or it must be a Java class such as java.lang.String.

The Java arrays are passed to Java methods by reference, so the elements of the array can be manipulated in Java. Furthermore, Java arrays can be created in Java code and returned to the Genero program.

This example shows how to create a Java array in Genero, to instantiate a Java Array of INTEGER elements:

MAIN
  TYPE int_array_type ARRAY[] OF INTEGER
  DEFINE ja int_array_type
  LET ja = int_array_type.create(100)
  LET ja[10] = 123
  DISPLAY ja[10], ja[20]
  DISPLAY ja.getLength()
END MAIN

This example shows a program creating a Java array of Java strings:

IMPORT JAVA java.lang.String
MAIN
    TYPE string_array_type ARRAY[] OF java.lang.String
    DEFINE names string_array_type
    LET names = string_array_type.create(100)
    LET names[1] = "aaaaaaa"
    DISPLAY names[1]
END MAIN

To create a Java array of structured RECORD elements, use the com.fourjs.fgl.lang.FglRecord class:

IMPORT JAVA com.fourjs.fgl.lang.FglRecord
MAIN
  TYPE record_array_type ARRAY[]
       OF com.fourjs.fgl.lang.FglRecord
  DEFINE ra record_array_type
  TYPE r_t RECORD
       id INTEGER,
       name VARCHAR(100)
      END RECORD
  DEFINE r r_t
  LET ra = record_array_type.create(100)
  LET r.id = 123
  LET r.name = "McFly"
  LET ra[10] = r
  INITIALIZE r TO NULL
  LET r = CAST (ra[10] AS r_t)
  DISPLAY r.*
END MAIN

Java arrays of Java classes can be defined. This example introspects the java.lang.String class by using Java array of java.lang.reflect.Method to query the list of methods from the java.lang.String class:

IMPORT JAVA java.lang.Class
IMPORT JAVA java.lang.reflect.Method
MAIN
  DEFINE c java.lang.Class
  DEFINE ma ARRAY[] OF java.lang.reflect.Method
  DEFINE i INTEGER
  LET c = Class.forName("java.lang.String")
  LET ma = c.getMethods()
  FOR i = 1 TO ma.getLength()
     DISPLAY ma[i].toString()
  END FOR
END MAIN

Java arrays can be created in the Java code, to be returned from a method and assigned to a program variable:

public static int [] createIntegerArray(int size) {
    return new int[size];
}