[英]Basic addition and subtraction with choices
Please help with this. 请帮忙。 I am very new to this, and I need this badly. 我对此很陌生,我非常需要这个。 I need to create a program where it lets you choose from addition or subtraction. 我需要创建一个程序,让您从加法或减法中进行选择。 This is my current program: 这是我当前的程序:
import javax.swing.JOptionPane;
public class RationalZ {
public static void main(String args[]) {
JOptionPane.showMessageDialog(null,
"Enter the letter A for Addition and B Subtraction");
String choice = JOptionPane.showInputDialog(
"A=Addition B=Subtraction");
if (choice == "a") {
String strNum1 = JOptionPane.showInputDialog(
"Enter a Number");
String strNum2 = JOptionPane.showInputDialog(
"Enter a second number");
int aNum1 = Integer.parseInt(strNum1);
int aNum2 = Integer.parseInt(strNum2);
JOptionPane.showMessageDialog(null, aNum1 + aNum2);
System.exit(0);
} else {
System.exit(0);
}
}
}
What's wrong? 怎么了? Even in the first step I can't get it. 即使是第一步,我也无法理解。
You might want to review the difference between the ==
operator and the equals()
method. 您可能需要查看==
运算符和equals()
方法之间的区别。
Addendum: It's fairly easy to find good information on Java String
comparison methods ; 附录:在Java String
比较方法中找到好的信息相当容易; it's a little harder to find a good explanation of why ==
with String
is usually wrong. 很难找到一个很好的解释 ,为什么用String
==
通常是错误的。
Addendum: 附录:
Do I use another if statement? 我是否要使用另一个if语句?
You've got a good if-then
statement; 您有一个很好的if-then
语句; now you need to expand it to an if-then-else statement. 现在,您需要将其扩展为if-then-else语句。 Notice how you can add more if-then
statements after the else
. 注意如何在else
后面添加更多if-then
语句。
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