javafx写的计算自由落体小程序

import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.geometry.HPos;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.TextField;
import javafx.scene.layout.GridPane;
import javafx.scene.text.Text;
import javafx.stage.Stage;

import java.util.regex.Pattern;

public class Main extends Application {
    
    
    double a;
    int k=5;
    String str;
    public static void main(String[] args) {
    
    
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) throws Exception {
    
    

        TextField textField1 = new TextField("");
        TextField textField2 = new TextField("");
        TextField textField3 = new TextField("");
        Text t1 = new Text("高度(m) = ");
        Text t2 = new Text("下落时间(s) = ");
        Text t3 = new Text("保留小数位(默认5) = ");

        //文本框里的灰色提示
        textField1.setPromptText("请输入高度");
        textField2.setPromptText("请输入时长");
        textField3.setPromptText("结果保留小数位数");
        //设置焦点
        textField1.setFocusTraversable(false);
        textField2.setFocusTraversable(false);
        textField3.setFocusTraversable(false);

        //网格布局
        GridPane gridPane = new GridPane();
        gridPane.add(t1,0,0);
        gridPane.add(textField1,1,0);
        gridPane.add(t2,0,1);
        gridPane.add(textField2,1,1);
        gridPane.add(t3,0,2);
        gridPane.add(textField3,1,2);
        //布局对齐
        gridPane.setAlignment(Pos.TOP_CENTER);

        //布局的内边距
        gridPane.setPadding(new Insets(10,10,10,0));

        //场景
        Scene scene = new Scene(gridPane);

        //组件的外边距
        GridPane.setMargin(t1,new Insets(10));
        GridPane.setMargin(t2,new Insets(10));
        GridPane.setMargin(t3,new Insets(10));

        //调整组件对齐
        GridPane.setHalignment(t1, HPos.RIGHT);
        GridPane.setHalignment(t2, HPos.RIGHT);
        GridPane.setHalignment(t3, HPos.RIGHT);

        //添加监听
        //监听内容变化
        textField1.textProperty().addListener(new ChangeListener<String>() {
    
    
            @Override
            public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
    
    
                if(textField1.isFocused()){
    
    
                    //过滤出数字
                    str = Pattern.compile("[^0-9]").matcher(newValue).replaceAll("");
                    //啥都不填 a=0
                    if(str.equals("")) {
    
     textField2.clear(); a = 0;}
                    //正常情况
                    else {
    
    
                        a = Double.parseDouble(str);
                        textField2.setText(String.valueOf(String.format("%." + k + "f", Math.pow(2 * a / 9.8, 0.5))));
                    }
                }

            }
        });

        textField2.textProperty().addListener(new ChangeListener<String>() {
    
    
            @Override
            public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
    
    
                if(textField2.isFocused()) {
    
    
                    str = Pattern.compile("[^0-9]").matcher(newValue).replaceAll("");
                    if (str.equals("")) {
    
     textField1.clear(); a = 0;}
                    else {
    
    
                        a = Double.parseDouble(str);
                        textField1.setText(String.valueOf(String.format("%." + k + "f", 0.5 * 9.8 * Math.pow(a, 2))));
                    }
                }
            }
        });

        textField3.textProperty().addListener(new ChangeListener<String>() {
    
    
            @Override
            public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
    
    
                str = Pattern.compile("[^0-9]").matcher(newValue).replaceAll("");
                if(str.equals("")) {
    
     k=5; }
                else if(!textField2.getText().isEmpty()) {
    
    
                    k = Integer.parseInt(str);
                }
                textField2.setText(String.valueOf(String.format("%." + k + "f", Math.pow(2 * a / 9.8, 0.5))));

            }
        });

        primaryStage.setTitle("计算自由落体");
        primaryStage.setScene(scene);
        primaryStage.setHeight(200);
        primaryStage.setWidth(400);
        primaryStage.show();
    }
}

效果：

修改一个bug后的版本：

package Demo1;

import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.geometry.HPos;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.TextField;
import javafx.scene.layout.GridPane;
import javafx.scene.text.Text;
import javafx.stage.Stage;

import java.util.regex.Pattern;

public class Main extends Application {
    
    
    double a;
    int k=5;
    int which=1;//改哪个框里的内容
    String str;
    public static void main(String[] args) {
    
    

        launch(args);
    }

    @Override
    public void start(Stage primaryStage) throws Exception {
    
    

        TextField textField1 = new TextField("");
        TextField textField2 = new TextField("");
        TextField textField3 = new TextField("");
        Text t1 = new Text("高度(m) = ");
        Text t2 = new Text("下落时间(s) = ");
        Text t3 = new Text("保留小数位(默认5) = ");

        //文本框里的灰色提示
        textField1.setPromptText("请输入高度");
        textField2.setPromptText("请输入时长");
        textField3.setPromptText("结果保留小数位数");
        //设置焦点
        textField1.setFocusTraversable(false);
        textField2.setFocusTraversable(false);
        textField3.setFocusTraversable(false);

        //网格布局
        GridPane gridPane = new GridPane();
        gridPane.add(t1,0,0);
        gridPane.add(textField1,1,0);
        gridPane.add(t2,0,1);
        gridPane.add(textField2,1,1);
        gridPane.add(t3,0,2);
        gridPane.add(textField3,1,2);
        //布局对齐
        gridPane.setAlignment(Pos.TOP_CENTER);

        //布局的内边距
        gridPane.setPadding(new Insets(10,10,10,0));

        //场景
        Scene scene = new Scene(gridPane);

        //组件的外边距
        GridPane.setMargin(t1,new Insets(10));
        GridPane.setMargin(t2,new Insets(10));
        GridPane.setMargin(t3,new Insets(10));

        //调整组件对齐
        GridPane.setHalignment(t1, HPos.RIGHT);
        GridPane.setHalignment(t2, HPos.RIGHT);
        GridPane.setHalignment(t3, HPos.RIGHT);

        //添加监听
        //监听内容变化
        textField1.textProperty().addListener(new ChangeListener<String>() {
    
    
            @Override
            public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
    
    
                if(textField1.isFocused()){
    
    
                    //过滤出数字
                    str = Pattern.compile("[^0-9]").matcher(newValue).replaceAll("");
                    //啥都不填 a=0
                    if(str.equals("")) {
    
     textField2.clear(); a = 0;}
                    //正常情况
                    else {
    
    
                        a = Double.parseDouble(str);
                        textField2.setText(String.valueOf(String.format("%." + k + "f", Math.pow(2 * a / 9.8, 0.5))));
                    }
                    which = 2;
                }

            }
        });

        textField2.textProperty().addListener(new ChangeListener<String>() {
    
    
            @Override
            public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
    
    
                if(textField2.isFocused()) {
    
    
                    str = Pattern.compile("[^0-9]").matcher(newValue).replaceAll("");
                    if (str.equals("")) {
    
     textField1.clear(); a = 0;}
                    else {
    
    
                        a = Double.parseDouble(str);
                        textField1.setText(String.valueOf(String.format("%." + k + "f", 0.5 * 9.8 * Math.pow(a, 2))));
                    }
                    which = 1;
                }
            }
        });

        textField3.textProperty().addListener(new ChangeListener<String>() {
    
    
            @Override
            public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
    
    
                str = Pattern.compile("[^0-9]").matcher(newValue).replaceAll("");
                if(str.equals("")) {
    
     k=5; }
                else if(!textField2.getText().isEmpty()) {
    
    
                    k = Integer.parseInt(str);
                }
                if(which == 2)
                    textField2.setText(String.valueOf(String.format("%." + k + "f", Math.pow(2 * a / 9.8, 0.5))));
                else
                    textField1.setText(String.valueOf(String.format("%." + k + "f", Math.pow(2 * a / 9.8, 0.5))));
            }
        });

        primaryStage.setTitle("计算自由落体");
        primaryStage.setScene(scene);
        primaryStage.setHeight(200);
        primaryStage.setWidth(400);
        primaryStage.show();
    }
}

bug是修改"保留小数位数"时没判断焦点而引起的。因为要判断的焦点是在焦点落到textField3前一次的焦点，比较繁琐，于是增加了一个其它的判断条件。