Programming Flix

Creating Objects

We can import the constructor of a Java class as a Flix function and use it to construct new objects.

For example:

import java_new java.io.File(String): ##java.io.File \ IO as newFile;
newFile("HelloWorld.txt")

Here we import the constructor of the java.io.File class and give it the local name newFile. The newFile function takes a string argument and returns a fresh Java File object. Constructing a fresh object is impure, hence main is marked as having the IO effect.

When we import a constructor, we must specify the types of its formal parameters. This is required because Java supports constructor overloading (i.e. a class may have multiple constructors only distinguished by their formal parameters.)

For example, the java.io.File class has another constructor that takes two arguments: one for the parent pathname and one for the child pathname. We can use this constructor as follows:

import java_new java.io.File(String, String): ##java.io.File \ IO as newFile;
newFile("foo", "HelloWorld.txt")

Here the import describes that the constructor expects two String arguments.

Note: import statements must occur at the expression-level, i.e. they must occur inside a function. Unlike use declarations, they cannot occur at top of a module.