Java: NoSuchMethodException with reflection when method clearly exists

I've been trying to use Reflection in Java, Here's my code:

String charsetName = "UTF-16LE";
java.nio.charset.CharsetDecoder cd = Charset.forName(charsetName).newDecoder();

Class c = cd.getClass();

Class[] paramTypes = new Class[] {ByteBuffer.class, CharBuffer.class };

try {
     Method method = c.getDeclaredMethod("decodeLoop", paramTypes);
     method.setAccessible(true);
     assertTrue(true);
} catch (NoSuchMethodException | SecurityException e) {
     e.printStackTrace();
     assertTrue(false);
}

Method clearly exists. Java source:

package java.nio.charset;

public abstract class CharsetDecoder {
...
   protected abstract CoderResult decodeLoop(ByteBuffer in,
                                          CharBuffer out);
...
}

The output:

java.lang.NoSuchMethodException:   sun.nio.cs.UTF_16LE$Decoder.decodeLoop(java.nio.ByteBuffer, java.nio.CharBuffer)
at java.lang.Class.getDeclaredMethod(Class.java:2130)
at com.krasutski.AppTest.testDeclaredMethod(AppTest.java:227)
...

if I use a parameter charsetName as

• "UTF-16LE" - Exception NoSuchMethodException
• "UTF-16BE" - Exception NoSuchMethodException
• "UTF-8" - Very good
• "cp1252" - Very good

How I'm supposed to fix this?