Java - 使用异常答案

【问题标题】：Java - using ExceptionsJava - 使用异常
【发布时间】：2016-04-07 22:09:40
【问题描述】：

添加数字时，我需要使用异常处理来捕获不正确的数值。我有我创建的代码，但我不知道该怎么做。有人可以告诉我它是如何正确完成的，以便我知道未来。

import javafx.application.Application;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.*;

import javafx.scene.layout.*;
import javafx.event.*;
import javafx.stage.Stage;

public class test33 extends Application {
    private double num1 = 0, num2 = 0, result = 0;

  @Override
  // Override the start method in the Application class
  public void start(Stage primaryStage) {
    FlowPane pane = new FlowPane();
    pane.setHgap(2);
    TextField tfNumber1 = new TextField();
    TextField tfNumber2 = new TextField();
    TextField tfResult = new TextField();

    tfNumber1.setPrefColumnCount(3);
    tfNumber2.setPrefColumnCount(3);
    tfResult.setPrefColumnCount(3);

    pane.getChildren().addAll(new Label("Number 1: "), tfNumber1,
      new Label("Number 2: "), tfNumber2, new Label("Result: "), tfResult);

    // Create four buttons
    HBox hBox = new HBox(5);
    Button btAdd = new Button("Add");

    hBox.setAlignment(Pos.CENTER);
    hBox.getChildren().addAll(btAdd);

    BorderPane borderPane = new BorderPane();
    borderPane.setCenter(pane);
    borderPane.setBottom(hBox);
    BorderPane.setAlignment(hBox, Pos.TOP_CENTER);

    // Create a scene and place it in the stage
    Scene scene = new Scene(borderPane, 375, 150);
    primaryStage.setTitle("Test33"); // Set the stage title
    primaryStage.setScene(scene); // Place the scene in the stage
    primaryStage.show(); // Display the stage

    btAdd.setOnAction(new EventHandler<ActionEvent>() {

        public void handle(ActionEvent e) {
            num1 = Double.parseDouble(tfNumber1.getText());
            num2 = Double.parseDouble(tfNumber2.getText());
            result = num1 + num2;
            tfResult.setText(String.format("%.1f", result)); 
        }
    });



  }

  /**
   * 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);
  }
}

【问题讨论】：

什么是“不正确的数值”？只是它不是某种数字（例如，在 tfNumber1 中输入“asdf”）？还是有其他考虑（例如，不能为负数）？

标签： java exception javafx exception-handling

【解决方案1】：

应该存在的异常处理的一个方面是在.parseDouble() 中。我建议至少添加 NumberFormatException 处理

     public void handle(ActionEvent e) {
        try {
          num1 = Double.parseDouble(tfNumber1.getText());
          num2 = Double.parseDouble(tfNumber2.getText());
          result = num1 + num2;
          tfResult.setText(String.format("%.1f", result)); 
        } 
        catch (NumberFormatException nfe) {
           tfResult.setText("Invalid input!");
        }
    }

可以通过捕获导致错误的特定输入等来获得更细粒度。但是，从捕获错误数字的演示角度来看，此代码是说明性的。

【讨论】：