Java - 菜单选择的 While 循环（基于控制台的程序）
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Java - While loop for menu selection (console based program)
提问by Dave
UpdateThe first time the user makes a choice such as "1" the menu is displayed again. The next time a selection is made the payment information begins to cycle. After the cycling is complete and the menu is displayed again, it works as it should. Also, the first two years are output instead of just the first when a selection begins to cycle, but then outputs one year at a time as intended.
更新用户第一次做出选择（例如“1”）时，菜单会再次显示。下次做出选择时，支付信息开始循环。循环完成并再次显示菜单后，它可以正常工作。此外，前两年是输出而不是选择选择开始周期的第一个，但随后将在预期的时间输出一年。
//create scanner object for choosing a loan, then prompt for and accept input
Scanner choose = new Scanner(System.in);
String choice;
System.out.println("\nType 1, 2, or 3 and press enter to see the monthly payment information for the respective loan. To end the program type \"end\".");
choice = choose.next();
//cycle loan 1 payment information
//create scanner object to advance to the next year's payments
//loop for cycling payment information
//initialize loan principal to variable
while (!"end".equals(choice)) {
System.out.println("\nType 1, 2, or 3 and press enter to see the monthly payment information for the respective loan. To end the program type \"end\".");
choice = null;
choice = choose.next();
if ("1".equals(choice)) {
//calculation code
}
if (j < 6) {
System.out.println("Press enter to get the mortgage information for year " + (j + 2));
choice = choose.nextLine();
} else {
System.out.println("Congratulations, your mortgage has been paid off.");
}
}
choice = null;
}
if ("2".equals(choice)) {
//calculation code
}
if (j < 14) {
System.out.println("Press enter to get the mortgage information for year " + (j + 2));
choice = choose.nextLine();
} else {
System.out.println("Congratulations, your mortgage has been paid off.");
}
}
choice = null;
}
if ("3".equals(choice)) {
//calculation code
}
if (j < 29) {
System.out.println("Press enter to get the mortgage information for year " + (j + 2));
choice = next.nextLine();
} else {
System.out.println("Congratulations, your mortgage has been paid off.");
}
}
choice = null;
}
}
choose.close();
}
}
}
回答by Yogendra Singh
I can see three issues upfront:
我可以预先看到三个问题：
You don't need two scanners for
System.instream. Remove this statementScanner next = new Scanner(System.in);and use thechooseinstance.If you close your input scanner as
next.close();, it closes your input streamSystem.inas well and you may not be able read the stream again. Make sure you close the stream only when you are completely done with your program.Use
equalsmethod to compare the condition inwhileaswhile(!"end".equals(choice)). Put the literal"end"as first argument will take care of the null value ofchoice.
您不需要两个扫描仪进行
System.in流媒体播放。删除此语句Scanner next = new Scanner(System.in);并使用choose实例。如果您将输入扫描器
next.close();关闭为，它System.in也会关闭您的输入流，您可能无法再次读取该流。确保仅在您完全完成程序后才关闭流。使用
equals方法比较whileas 中的条件while(!"end".equals(choice))。将文字"end"作为第一个参数将处理choice.
EDIT:
编辑：
Your modified code at high level:
您修改后的高级代码：
Scanner choose = new Scanner(System.in);
String choice= null;
int j = 0;
while (!"end".equals(choice)) {
System.out.println("\nType 1, 2, or 3 and press enter to see the monthly payment information for the respective loan. To end the program type \"end\".");
choice = choose.nextLine();
if ("1".equals(choice)) {
//calculation code
if (j < 6) {
System.out.println("Press enter to get the mortgage information for year " + (j + 2));
choice = choose.nextLine();
} else {
System.out.println("Congratulations, your mortgage has been paid off.");
}
choice = null;
}
if ("2".equals(choice)) {
if (j < 14) {
System.out.println("Press enter to get the mortgage information for year " + (j + 2));
choice = choose.nextLine();
} else {
System.out.println("Congratulations, your mortgage has been paid off.");
}
choice = null;
}
if ("3".equals(choice)) {
if (j < 29) {
System.out.println("Press enter to get the mortgage information for year " + (j + 2));
choice = choose.nextLine();
} else {
System.out.println("Congratulations, your mortgage has been paid off.");
}
choice = null;
}
}
choose.close();
回答by awolfe91
One bug is that String equality isn't the same as ==. You should use .equals():
一个错误是字符串相等性与 == 不同。你应该使用 .equals():
while (!choice.equals("end")) {
Hope that helps!
希望有帮助！
回答by Soumya
You're setting choiceto null, so choice != "end"is always true.
Move the next.close(); choice = nullto outsidethe while loop.
Also, what weolfe91 said.
您设置choice为null，所以choice != "end"总是如此。将next.close(); choice = nullto 移到while 循环之外。还有，weolfe91 说的。
回答by sandeep shukla
import java.util.Scanner;
导入 java.util.Scanner;
class Main
主类
{
{
public static void main(String [] args)
{
Scanner sc=new Scanner(System.in);
System.out.println("Enter no.1:");
int a=sc.nextInt();
System.out.println("Enter no.2:");
int b=sc.nextInt();
boolean exit=false;
do
{
System.out.println("1.addition");
System.out.println("2.subtraction");
System.out.println("3.multiplication");
System.out.println("4.division");
System.out.println("5.exit");
System.out.println("choose one!");
Scanner sd=new Scanner(System.in);
System.out.println("enter your choice");
int num=sd.nextInt();
switch(num)
{
case 1:
int add=a+b;
System.out.println("addition="+add);
System.out.println("\n");
break;
case 2:
int sub=a-b;
System.out.println("subtraction="+sub);
System.out.println("\n");
break;
case 3:
int mul=a*b;
System.out.println("multilpication="+mul);
System.out.println("\n");
break;
case 4:
int div=a/b;
System.out.println("division="+div);
System.out.println("\n");
break;
case 5:
exit=true;
break;
}
}while(!exit);
}
}
}
