A Powerful addition to BoxLang’s Java interoperability!

We're excited to announce we’ve added more goodies to our BoxLang Java interop: method references and higher-order functions. These enhancements elevate Java integration, making your development experience more powerful and seamless than ever before.

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Java Method References

In CFML, you can grab a reference to a UDF or closure, pass it around, and invoke it. BoxLang extends this to Java methods, both instance and static. Check this out:

myInstance = new myClass();
myInstanceMethod = myInstance.myMethod;
myInstanceMethod();

And for static methods:

myStaticUDF = src.test.java.TestCases.phase3.StaticTest::sayHello;
myStaticUDF();

Treating Java Methods as Objects

In BoxLang, Java methods (both instance and static) are objects you can pass around, invoke, and use in higher-order functions. When you reference a method on a Java class without parentheses, you get a special Function instance. This lets you treat the method like any other function.

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Static Method Reference Example

Capture the static valueOf() method from the Java String class and invoke it:

import java:java.lang.String;
javaStaticMethod = java.lang.String::valueOf;
result = javaStaticMethod("test"); // New string of "test"

Instance Method Reference Example

Capture the toUpperCase method from a String instance:

javaInstanceMethod = "my string".toUpperCase;
result = javaInstanceMethod(); // "MY STRING"

Using Java Methods with Higher-Order Functions

BoxLang lets you use Java methods directly in place of UDFs or closures for higher-order functions. For example, sort an array in reverse order using Java’s Collections.reverseOrder().compare method:

import java.util.Collections;
[1, 7, 3, 99, 0].sort(Collections.reverseOrder().compare); // [99, 7, 3, 1, 0]

Limitations and Considerations

There are some limitations. Many Java methods can’t be used with CF/BL’s reduce, each, map higher-order built-in functions (BIFs) because they strictly enforce the number of arguments. For example:

import java:java.lang.Math;
[1, 2.4, 3.9, 4.5].map(Math::floor); // Error because floor only accepts a single arg!

The Math.floor() method accepts a single argument, but arrayMap() passes three arguments, causing an error.

Two-Way Compatibility with Java

BoxLang’s ability to pass closures into Java methods that accept functional interfaces or lambdas enhances two-way compatibility between Java and BoxLang. Check out this example of using a Java Stream with a BoxLang lambda:

fruits = ["apple", "banana", "cherry", "ananas", "elderberry"];
result = fruits.stream()
  .filter(fruit -> fruit.startsWith("a"))
  .toList();

Here, we convert a BoxLang array into a Java Stream, use the Java filter() method with a BoxLang lambda, and collect the results into a list.

Conclusion

With BoxLang’s new support for Java method references and higher-order functions, Java interop just got a whole lot cooler. This feature lets you write cleaner, more powerful code by leveraging Java’s capabilities within BoxLang’s modern syntax. Give it a try and see how it can boost your development experience!

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