samples/LambdaAsFunc.java

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import javax.script.*;
import java.util.function.*;

// example demonstrating that arbitrary Lambda can be called as function from script

public class LambdaAsFunc {
    public static void main(String[] args) throws Exception {
        ScriptEngineManager m = new ScriptEngineManager();
        ScriptEngine e = m.getEngineByName("nashorn");

        // expose a lambda as top-level script function
        e.put("upper", (Function<String, String>) String::toUpperCase);

        // call lambda as though it is a normal script function
        System.out.println(e.eval("upper('hello')"));
    }
}