使用if else语句调用不同的类

Question

我正在编写一个java程序，它就像一堂物理课：

import javax.swing.JOptionPane;
public class PhysicsClass {


    public static void main(String[] args) {
        int g = -1;
        while (g<0){
            String input = JOptionPane.showInputDialog("Welcome! What's your name? ");
            if(input.length() > 0){
                g++;
             System.out.println("Great! Lets begin.");
            }
            else{
                 System.out.println(" ok then.");
                System.exit(0);
            }
        }

         String[] firstChoice = {"Kinematics", "Dynamics", "Impulse/Momentum", "Energy/Power"}; 
            JOptionPane.showInputDialog(null,
                    "Which one of these Topic would you like to start with?", 
                    "Please pick a topic to start with",
                    JOptionPane.INFORMATION_MESSAGE, null,
                    firstChoice, firstChoice[0]);


            int i = 0;
            while (i<0){
            String Choice = "";
            if (Choice == firstChoice[0]){
             Kinematics.IntroToKinematics();
             i++;

            }
            else if (Choice == firstChoice[1]){
                Dynamics.DynamicsIntro();
             i++;
            }
            else if (Choice == firstChoice[2]){
                ImpulseAndMomentum.ImpulseAndMomentumIntro();
             i++;
            }
            else if (Choice == firstChoice[3]){
                EnergyAndPower.EnergyAndPowerIntro();
             i++;
            }
            else{
                System.out.println("Please pick one.");
            }
            }

我希望您在第一个选择数组中选择任何选项，然后转到受人尊敬的类。因此，如果我选择运动学，它将调用运动学类，它的前几行是：

import javax.swing.JOptionPane;

public class Kinematics {

    public static void IntroToKinematics() {
        JOptionPane.showInternalMessageDialog(null, "Kinematics is one of the most basic"
                + " ideas of Newtonian Physics. It encompasses: speed, distance, time"
                + " displacement, acceleration and many key base concepts that form the the "
                + " foundation for most physic subjects. It will poke its head in everything"
                + "we cover.", "intro", JOptionPane.INFORMATION_MESSAGE);
    }

}

它没有给我任何错误，但是当我从数组中选择一个字符串时，它没有做任何事情。我认为这可能与我使用的if else语句有关。感谢大家的帮助，我对Java还是比较陌生的，所以任何建议都将不胜感激。

Answer 1

使用equals比较字符串，如-

if(Choice.equals(firstChoice[0])){...}

Answer 2

首先，您希望将输入框的结果存储在某个位置：

String choice = JOptionPane.showInputDialog(null,
                "Which one of these Topic would you like to start with?", 
                "Please pick a topic to start with",
                JOptionPane.INFORMATION_MESSAGE, null,
                firstChoice, firstChoice[0]);

然后用.equals代替==进行字符串比较

if (choice.equals(firstChoice[0])){
     Kinematics.IntroToKinematics();
}

循环应该不是必需的。

Answer 3

您没有将选项绑定到选定的值，它总是将其与"“