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import jdk.nashorn.api.scripting.AbstractJSObject;
import java.nio.DoubleBuffer;
/**
 * Simple class demonstrating pluggable script object
 * implementation. By implementing jdk.nashorn.api.scripting.JSObject
 * (or extending AbstractJSObject which implements it), you
 * can supply a friendly script object. Nashorn will call
 * 'magic' methods on such a class on 'obj.foo, obj.foo = 33,
 * obj.bar()' etc. from script.
 *
 * In this example, Java nio DoubleBuffer object is wrapped
 * as a friendly script object that provides indexed acces
 * to buffer content and also support array-like "length"
 * readonly property to retrieve buffer's capacity. This class
 * also demonstrates a function valued property called "buf".
 * On 'buf' method, we return the underlying nio buffer object
 * that is being wrapped.
 */
public class BufferArray extends AbstractJSObject {
    // underlying nio buffer
    private final DoubleBuffer buf;
    public BufferArray(int size) {
        buf = DoubleBuffer.allocate(size);
    }
    public BufferArray(DoubleBuffer buf) {
        this.buf = buf;
    }
    // called to check if indexed property exists
    @Override
    public boolean hasSlot(int index) {
        return index > 0 && index < buf.capacity();
    }
    // get the value from that index
    @Override
    public Object getSlot(int index) {
       return buf.get(index);
    }
    // set the value at that index
    @Override
    public void setSlot(int index, Object value) {
       buf.put(index, ((Number)value).doubleValue());
    }
    // do you have a property of that given name?
    @Override
    public boolean hasMember(String name) {
       return "length".equals(name) || "buf".equals(name);
    }
    // get the value of that named property
    @Override
    public Object getMember(String name) {
       switch (name) {
          case "length":
              return buf.capacity();
          case "buf":
              // return a 'function' value for this property
              return new AbstractJSObject() {
                  @Override
                  public Object call(Object thiz, Object... args) {
                      return BufferArray.this.buf;
                  }
                  // yes, I'm a function !
                  @Override
                  public boolean isFunction() {
                      return true;
                  }
              };
       }
       return null;
    }
}

// Usage: jjs -scripting -cp . jsobject.js
// This sample demonstrats how to expose a
// script friendly object from your java code
// by implementing jdk.nashorn.api.scripting.JSObject
// compile the java program
`javac BufferArray.java`
// print error, if any and exit
if ($ERR != '') {
    print($ERR)
    exit($EXIT)
}
// create BufferArray
var BufferArray = Java.type("BufferArray")
var bb = new BufferArray(10)
// 'magic' methods called to retrieve set/get
// properties on BufferArray instance
var len = bb.length
print("bb.length = " + len)
for (var i = 0; i < len; i++) {
    bb[i] = i*i
}
for (var i = 0; i < len; i++) {
    print(bb[i])
}
// get underlying buffer by calling a method
// on BufferArray magic object
// 'buf' is a function member
print(typeof bb.buf)
var buf = bb.buf()
// use retrieved underlying nio buffer
var cap = buf.capacity()
print("buf.capacity() = " + cap)
for (var i = 0; i < cap; i++) {
   print(buf.get(i))
}