How to fix an error when trying to create a synthesizer (Java)?

Question

Java

Hello!
I recently started learning Java. Now I'm trying to implement an example from a book.
IDE - eclipce I
create as follows:

import javax.sound.midi.*;
import java.io.*;
import java.util.*;
public class MusicTest1 {
  public void play(){
        Sequencer sequencer = MidiSystem.getSequencer();
      System.out.println("Мы получили синтезатор");

  }
  public static void main(String[] args){
    MusicTest1 mt = new MusicTest1();
    mt.play();
  }
}

I get:
Exception in thread "main" java.lang.Error: Unresolved compilation problems:
sequencer cannot be resolved to a variable
MidiSystem cannot be resolved
What am I doing wrong?
_____________________________
Thank you all. Figured it out myself. In eclipce, in the project tree, it was necessary to delete and add the jre system Library.
After this operation, the compiler stopped "swearing" at the Sequencer type.