I use Windows and I used JGrasp to save this code. The code you see below is perfect and correct (except I added a package name on the top of each class), because it is example code I took off a powerpoint which was made from the course textbook we use. It is a program where a 客户 has to type a circle radius, the server receives the client s circle radius and then calculates the circle area, sending the cirlce area back to the client. How do I compile AND run this program in command prompt? I never learned about java packages before by the way.

服务器

package program;
import java.io.*;
import java.net.*;
import java.util.Date;
import javafx.application.Application;
import javafx.application.Platform;
import javafx.scene.Scene;
import javafx.scene.control.ScrollPane;
import javafx.scene.control.TextArea;
import javafx.stage.Stage;

public class 服务器 extends Application {
  @Override // Override the start method in the Application class
  public void start(Stage primaryStage) {
    // Text area for displaying contents
    TextArea ta = new TextArea();

    // Create a scene and place it in the stage
    Scene scene = new Scene(new ScrollPane(ta), 450, 200);
    primaryStage.setTitle("服务器"); // Set the stage title
    primaryStage.setScene(scene); // Place the scene in the stage
    primaryStage.show(); // Display the stage

    new Thread( () -> {
      try {
        // Create a server socket
        服务器Socket serverSocket = new 服务器Socket(8000);
        Platform.runLater(() ->
          ta.appendText("服务器 started at " + new Date() +  
 ));

        // Listen for a connection request
        Socket socket = serverSocket.accept();

        // Create data input and output streams
        DataInputStream inputFrom客户 = new DataInputStream(
          socket.getInputStream());
        DataOutputStream outputTo客户 = new DataOutputStream(
          socket.getOutputStream());

        while (true) {
          // Receive radius from the client
          double radius = inputFrom客户.readDouble();

          // Compute area
          double area = radius * radius * Math.PI;

          // Send area back to the client
          outputTo客户.writeDouble(area);

          Platform.runLater(() -> {
            ta.appendText("Radius received from client: " 
              + radius +  
 );
            ta.appendText("Area is: " + area +  
 ); 
          });
        }
      }
      catch(IOException ex) {
        ex.printStackTrace();
      }
    }).start();
  }

  /**
   * The main method is only needed for the IDE with limited
   * JavaFX support. Not needed for running from the command line.
   */
  public static void main(String[] args) {
    launch(args);
  }
}

客户

package program;
import java.io.*;
import java.net.*;
import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.ScrollPane;
import javafx.scene.control.TextArea;
import javafx.scene.control.TextField;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;

public class 客户 extends Application {
  // IO streams
  DataOutputStream to服务器 = null;
  DataInputStream from服务器 = null;

  @Override // Override the start method in the Application class
  public void start(Stage primaryStage) {
    // Panel p to hold the label and text field
    BorderPane paneForTextField = new BorderPane();
    paneForTextField.setPadding(new Insets(5, 5, 5, 5)); 
    paneForTextField.setStyle("-fx-border-color: green");
    paneForTextField.setLeft(new Label("Enter a radius: "));

    TextField tf = new TextField();
    tf.setAlignment(Pos.BOTTOM_RIGHT);
    paneForTextField.setCenter(tf);

    BorderPane mainPane = new BorderPane();
    // Text area to display contents
    TextArea ta = new TextArea();
    mainPane.setCenter(new ScrollPane(ta));
    mainPane.setTop(paneForTextField);

    // Create a scene and place it in the stage
    Scene scene = new Scene(mainPane, 450, 200);
    primaryStage.setTitle("客户"); // Set the stage title
    primaryStage.setScene(scene); // Place the scene in the stage
    primaryStage.show(); // Display the stage

    tf.setOnAction(e -> {
      try {
        // Get the radius from the text field
        double radius = Double.parseDouble(tf.getText().trim());

        // Send the radius to the server
        to服务器.writeDouble(radius);
        to服务器.flush();

        // Get area from the server
        double area = from服务器.readDouble();

        // Display to the text area
        ta.appendText("Radius is " + radius + "
");
        ta.appendText("Area received from the server is "
          + area +  
 );
      }
      catch (IOException ex) {
        System.err.println(ex);
      }
    });

    try {
      // Create a socket to connect to the server
      Socket socket = new Socket("localhost", 8000);
      // Socket socket = new Socket("130.254.204.36", 8000);
      // Socket socket = new Socket("drake.Armstrong.edu", 8000);

      // Create an input stream to receive data from the server
      from服务器 = new DataInputStream(socket.getInputStream());

      // Create an output stream to send data to the server
      to服务器 = new DataOutputStream(socket.getOutputStream());
    }
    catch (IOException ex) {
      ta.appendText(ex.toString() +  
 );
    }
  }

  /**
   * The main method is only needed for the IDE with limited
   * JavaFX support. Not needed for running from the command line.
   */
  public static void main(String[] args) {
    launch(args);
  }
}