Requirements

You only need to have the Java JRE installed on your Lycia Development system because the Java interface utilizes the already compiled .class files or Java packages containing .class files. The location of the pool of Java classes is simply specified by a CLASSPATH variable or command line argument.

Importing a Java Class

To use a Java class within a 4GL program, you simply import it as a normal line of 4gl code using the following syntax:

IMPORT JAVA <ClassName>

Unique native data type handling

Another unique feature of Lycia’s Java interoperation is the data type handling. Data passing and retrieving (returning) to and from Java methods/objects does not require the use of any special non-4gl-standard data types. The entire data mapping operations including array handling are done transparently which allows the developer to use the standard native 4GL data types and syntax. 

Java Object definition, creation and scope

Java objects are defined just like any other 4gl data types by using the fully qualified class name for the data type. To create an instance, simply use the create() method.

The scope of a reference to a Java Class can be modular or global.

IMPORT JAVA java.lang.StringBuffer
...
DEFINE sb StringBuffer
LET sb = StringBuffer.create()

Lycia 4GL <-> Java data type mapping

We have got following Java Class

public class SimpleClass {
private int val;
public SimpleClass() {
}
public SimpleClass(int val) {
this.val = val;
}
public int getVal() {
return val;
}
public void setVal(int val) {
this.val = val;
}
public static int getValsSum(SimpleClass v1, SimpleClass v2){
return v1.getVal() + v2.getVal();
}
}

And together with the Java interface implementation, Lycia offers much more to make your applications universal and fit for any environment:

…and in this 4gl code, we will use our Java class:

IMPORT JAVA SimpleClass -- class is imported
MAIN
DEFINE s, s1 SimpleClass,
i, i1, param INT,
ii BIGINT,
ch CHAR

PROMPT "Enter the parameter for SimpleClass object s: "

FOR param

# constructor SimpleClass(int val) is invoked
LET s = SimpleClass.create(param)

# constructor SimpleClass() is invoked
LET s1=SimpleClass.create() 

# these are object methods without parameters
LET i=s.getVal()
LET i1=s1.getVal()
DISPLAY "The initial value of the object s  = ", i

AT 3,2
DISPLAY "The initial value of the object s1 = ", i1

AT 4,2

INITIALIZE param TO NULL
PROMPT "Enter the new value for SimpleClass object s1: "

FOR param

# this is an object methods with parameters
CALL s1.setVal(param)
LET i1=s1.getVal()
DISPLAY "The new value of the object s1 = ", i1 AT 4,2

# method getValSum is a class method,

# because it has 'static' keyword
LET ii = SimpleClass.getValsSum(s,s1)
DISPLAY "The getValPow() method returns: s1+s2 = ", ii

AT 6,2

PROMPT "Press any key to exit..." FOR CHAR ch
END MAIN