AWT KeyListener滯后於輸入

Question

我正在創建一個簡單的Java圓計算器，但是在使我的KeyListener快速響應時遇到了問題。 Circle類中的x和y值不會立即存儲，而是在刪除輸入時存儲。 例如，如果我為x輸入3，為y輸入5，Circle類將返回0的值，直到刪除這些值為止，然后它將返回正確的值。 我的目標是在用戶輸入值時立即顯示與此坐標相關的數據。 KeyListeners滯后時，我無法執行此操作。 謝謝。

**編輯：剛意識到如果我之后再按另一個鍵（例如ctrl），這些值也將是正確的

**第二次編輯：在底部添加了圈子代碼

**第三次編輯：在底部添加了點代碼

這是我的代碼：

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.text.DecimalFormat;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class CircleGUI extends JFrame
{
    Circle c;
    JFrame frame;
    DecimalFormat df;
    private JPanel panel;
    private JLabel radiusLabel, areaLabel, coordinateLabel, containsPointLabel;
    private JButton calculateButton;
    private JTextField radiusTextField, xTextField, yTextField;
    final int WINDOW_WIDTH = 500;
    final int WINDOW_HEIGHT = 300;

    public static void main(String[] args)
    {
        Circle c = new Circle();
        CircleGUI test = new CircleGUI(c);
    }

    public CircleGUI(Circle c)
    {
        this.c = c;
        setTitle("Circle Calculator");
        setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        buildPanel();

        add(panel);

        df = new DecimalFormat("#.##");

        setVisible(true);

    }

    private JPanel buildPanel()
    {
        radiusLabel = new JLabel("Enter radius:");

        areaLabel = new JLabel();

        radiusTextField = new JTextField(15);
        calculateButton = new JButton("Calculate Area");
        calculateButton.addActionListener(new CalculateAreaButtonListener());

        coordinateLabel = new JLabel("Origin of the Circle:");
        containsPointLabel = new JLabel("");
        xTextField = new JTextField(4);
        xTextField.addKeyListener(new xCoordinateTextFieldListener());
        yTextField = new JTextField(4);
        yTextField.addKeyListener(new yCoordinateTextFieldListener());

        panel = new JPanel();
        //panel.setLayout(new FlowLayout());
        panel.add(radiusLabel);
        panel.add(radiusTextField);
        panel.add(calculateButton);
        panel.add(areaLabel);
        panel.add(coordinateLabel);
        panel.add(xTextField);
        panel.add(yTextField);
        panel.add(containsPointLabel);

        return panel;
    }

    private class CalculateAreaButtonListener implements ActionListener
    {

        @Override
        public void actionPerformed(ActionEvent e)
        {
            areaLabel.setText(String.valueOf(df.format(calculateArea())));
        }

        public double calculateArea()
        {
            double radius = Double.parseDouble(radiusTextField.getText());
            c.setRadius(radius);
            return c.getArea();
        }

    }

    private class xCoordinateTextFieldListener implements KeyListener
    {

        @Override
        public void keyPressed(KeyEvent e)
        {
            double x;
            if (!xTextField.getText().equals(null) && !xTextField.getText().equals(""))
            {
                x = Double.parseDouble(xTextField.getText());
                c.setX(x);
            }

        }

        @Override
        public void keyReleased(KeyEvent e)
        {
            System.out.println("x: " + c.getX());
        }

        @Override
        public void keyTyped(KeyEvent arg0)
        {
        }

    }

    private class yCoordinateTextFieldListener implements KeyListener
    {

        @Override
        public void keyPressed(KeyEvent e)
        {

            double y;

            if (!yTextField.getText().equals(null) && !yTextField.getText().equals(""))
            {
                y = Double.parseDouble(yTextField.getText());
                c.setY(y);
            }
            ;

        }

        @Override
        public void keyReleased(KeyEvent e)
        {
            System.out.println("y: " + c.getY());
        }

        @Override
        public void keyTyped(KeyEvent arg0)
        {
        }

    }

}

圈子代碼：

    public class Circle
{

    //Instantiate and declare instance fields
    Point origin = new Point();
    double radius;

    Circle(double radius)
    {
        this.radius = radius;
        origin.setX(0);
        origin.setY(0);
    }



    //Two arg-constructor
    Circle(Point origin, double radius)
    {
        this.origin = origin;
        this.radius = radius;
    }

    //Three-arg constructor
    Circle(double xValue, double yValue, double radius)
    {
        origin.setX(xValue);
        origin.setY(yValue);
        this.radius = radius;
    }

    //Default constructor
    Circle()
    {
        setX(0);
        setY(0);
        radius = 0;
    }

    //Copy constructor
    Circle(Circle c)
    {
        setX(c.getX());
        setY(c.getY());
        radius = c.getRadius();
    }

    //Get origin of the circle
    Point getOrigin()
    {
        return origin;

    }

    //Set origin of the circle
    void setOrigin(Point point)
    {
        this.origin = point;
    }

    //Set x value
    void setX(double x)
    {
        origin.setX(x);
    }

    //Get x value
    double getX()
    {
        return origin.getX();
    }

    //Set y value
    void setY(double y)
    {
        this.origin.setY(y);
    }

    //Get y value
    double getY()
    {
        return origin.getY();
    }

    //Set radius field
    void setRadius(double radius)
    {
        this.radius = radius;
    }

    //Get radius field
    double getRadius()
    {
        return radius;
    }

    //Get area of the circle
    double getArea()
    {
        //Use constant provided in the static method Math.PI
        return Math.PI * (radius * radius);
    }

    //Translate instance fields to a human readable String
    public String toString()
    {
        return "x: " + this.getX() + ", y: " + this.getY() + ", radius: " + this.radius;
    }

    //Compare whether two circles instance fields are equal
    boolean equals(Circle c)
    {
        if (getX() == c.getX() && getY() == c.getY() && getRadius() == c.getRadius())
            return true;
        else
            return false;
    }

    double getDistance(double xValue, double yValue)
    {
        double x = xValue - this.getX();
        double y = yValue - this.getY();

        return Math.sqrt((x * x) + (y * y));
    }

    double getDistance(Circle c)
    {
        //Initialize variables to x^2-x^1 and y^2-y^1
        double x = c.getX() - this.getX();
        double y = c.getY() - this.getY();

        //Calculate distance to center of the circle
        return Math.sqrt((x * x) + (y * y));
    }

    boolean containsPoint(double xValue, double yValue)
    {
        if (getDistance(xValue, yValue) <= radius)
            return true;
        else
            return false;

    }

    //Test if two circle overlap
    boolean doesOverlap(Circle c)
    {
        //Initialize sumOfRadii to the sum of both circles radius
        double sumOfRadii = c.getRadius() + radius;

        //If the distance to the center of the circle is less than or equal to the sum of the two circles radius then return true, otherwise return false.
        if (getDistance(c) <= sumOfRadii)
            return true;
        else
            return false;
    }
}

點代碼：

public class Point
{

    private double x;
    private double y;

    public Point(double xValue, double yValue)
    {
        x = xValue;
        y = yValue;
    }

    public Point(Point p) {
        this(p.x, p.y);
    }

    public Point() {
        this(0, 0);
    }

    public void setX(double xValue)
    {
        this.x = xValue;
    }

    public double getX()
    {
        return x;
    } 

    public void setY(double yValue)
    {
        this.y = yValue;
    }

    public double getY()
    {
        return y;
    }

    public boolean equals(Point otherPoint)
    {
        return (this.x == otherPoint.x) && (this.y == otherPoint.y);
    }

    public String toString() {
        return "(" + x + ", " + y + ")";
    }
}

Answer 1

Keylistener不是響應文本字段中更改的正確選擇。 有關替代方法，請參見如何編寫文檔偵聽器 。

Answer 2

首先，我不會使用KeyListener來監視文本字段的更改， DocumentListener會為基礎字段的更改提供更多有用的信息，但是在這些情況下， ActionListener可能更合適。

看一看如何編寫動作偵聽器和如何使用文本字段以了解更多詳細信息