Write a Java applet which converts metres into kilometres and centimetres as given by the user.

Sure, here's a simple Java applet that converts meters into kilometers and centimeters as given by the user:

import java.awt.*;
import java.awt.event.*;
import java.applet.*;

public class LengthConverter extends Applet implements ActionListener {
    TextField meterField;
    Label resultLabel;

    public void init() {
        // Set layout
        setLayout(new GridLayout(3, 1));

        // Create input field for meters
        Label meterLabel = new Label("Enter length in meters:");
        meterField = new TextField(10);

        // Create button for conversion
        Button convertButton = new Button("Convert");
        convertButton.addActionListener(this);

        // Create label for displaying result
        resultLabel = new Label("");

        // Add components to the applet
        add(meterLabel);
        add(meterField);
        add(convertButton);
        add(resultLabel);
    }

    public void actionPerformed(ActionEvent ae) {
        // Get length in meters from user input
        String meterString = meterField.getText();
        double meters = Double.parseDouble(meterString);

        // Convert meters to kilometers and centimeters
        double kilometers = meters / 1000;
        double centimeters = meters * 100;

        // Display the result
        resultLabel.setText("Length in kilometers: " + kilometers + " km" +
                            ", Length in centimeters: " + centimeters + " cm");
    }
}

This applet creates a simple user interface with a text field for the user to enter the length in meters, a button to trigger the conversion, and a label to display the result. When the user clicks the "Convert" button, the length entered in meters is converted into kilometers and centimeters, and the result is displayed in the label.