java 使用案例后如何制作Java主菜单循环
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原文地址: http://stackoverflow.com/questions/34928182/
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How to make a Java Main Menu Loop after using a case
提问by Ace Ebert
I am pretty dang new to Java, but being familiar with some other programming languages, I know the basic lay out of a lot of it. One thing I am struggling with is looping menus, specifically a main menu.
我对 Java 非常陌生，但熟悉其他一些编程语言，我知道其中很多的基本布局。我正在努力解决的一件事是循环菜单，特别是主菜单。
I have tirelessly researched methods of it, but none seem to apply or work to my program. I'm assuming its something silly and small that I'm missing in my more-so basic program.
我不知疲倦地研究了它的方法，但似乎没有一种方法适用于或适用于我的程序。我假设我的基本程序中缺少它一些愚蠢和小的东西。
Check it below, thanks for any tips.
检查下面，感谢您的任何提示。
import java.util.Scanner;
public class basicCalc {
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner input = new Scanner(System.in);
boolean mainLoop = true;
int choice;
do{
System.out.println("Calculator Main Menu\n");
System.out.print("1.) Addition \n");
System.out.print("2.) Subtraction.\n");
System.out.print("3.) Multiplication.\n");
System.out.print("4.) Division.\n");
System.out.print("5.) Generate Random Number.\n");
System.out.print("6.) Exit\n");
System.out.print("\nEnter Your Menu Choice: ");
choice = input.nextInt();
}
while(choice >7);
switch(choice){
case 1:
//Definitions
int adNumf, adNuml, sum;
System.out.print("Please Enter The First Number: ");
adNumf = input.nextInt();
System.out.print("\nPlease Enter The Second Number: ");
adNuml = input.nextInt();
sum = adNumf + adNuml;
System.out.print("The Sum Of Those Numbers is: " +sum);
break;
case 2:
int subNum1, subNum2, sum2;
System.out.println("\nPlease Enter The First Number: ");
subNum1 = input.nextInt();
System.out.println("Please Enter The Second Number: ");
subNum2 = input.nextInt();
sum2 = subNum1 - subNum2;
System.out.println("The Subtraction Leaves The Number: " +sum2);
break;
case 3:
int multNum1, multNum2, multTotal;
// Gather Input
System.out.println("Please Enter The First Number To Multiply: ");
multNum1 = input.nextInt();
System.out.println("Please Enter The Second Number To Multiply: ");
multNum2 = input.nextInt();
// This will Multiply the Numbers
multTotal = multNum1 * multNum2;
//Display Final
System.out.println("The Multiplied Numbers Are: " +multTotal);
break;
case 4:
//Definitions
double divNum1, divNum2, divTotal;
System.out.println("Enter Your Numerator ");
divNum1 = input.nextInt();
System.out.println("Enter Your Denominator ");
divNum2 = input.nextInt();
if(divNum2 == 0){
System.out.println("Zero is Not divisable, please select a new denominator: ");
divNum2 = input.nextInt();
}
divTotal = divNum1 / divNum2;
System.out.println("Your divisor is: " +divTotal);
break;
case 5:
double limL, limH, rand;
System.out.println("Enter Your Low Limit: ");
limL = input.nextInt();
System.out.println("Enter Your High Limit ");
limH = input.nextInt();
//Equation to keep numbers within bounds
rand = limL + (Math.random() * ((limH - limL) + 1));
System.out.println("Given Your Limits, the Random Number will be: " +rand);
break;
case 6:
System.out.println("Exiting Program...");
System.exit(0);
break;
}
// Bad Menu Option Direct
if (choice > 6 || choice < 1){
System.out.println("This is not a valid Menu Option! Please Select Another.");
do{
choice = input.nextInt();
}
while(choice < 7 );
}
// End bad menu option
}
}
回答by Jimmy M.
You have a general idea of what to do, however you are making your loop ending condition more complicated than it needs to be. Try a "default" option to catch any input out of the range. That way you can simplify your ending condition to just "6" (the exit case). To show simply:
您对要做什么有一个大致的了解，但是您使循环结束条件比需要的更复杂。尝试使用“默认”选项来捕获超出范围的任何输入。这样您就可以将结束条件简化为“6”（退出情况）。简单地显示：
do{
//Menu options
System.out.print("6.) Exit\n");
System.out.print("\nEnter Your Menu Choice: ");
choice = input.nextInt();
switch(choice){
//Your cases from 1 to 6.
default:
System.out.println("Invalid menu choice; try again.");
break;
}
}while(choice != 6);
Whatever follows default will be called if the choice option is not for any of the cases create in your code.
如果选择选项不适用于您的代码中创建的任何案例，则将调用默认值之后的任何内容。
回答by The Law
Your whole execution flow is wrong. You should put the bad menu choice check (in your case the if) before the cases. And to have infinite menu loop, just add another ifthat breaks the infinite while-loop.
你的整个执行流程是错误的。您应该将错误的菜单选择检查（在您的情况下if）放在案例之前。并有无限菜单循环，只需添加另一个if打破无限的while-loop。
Pseudo code:
伪代码：
while(true){
//enter your choice, 8 to exit
if(choice != valid_range){
//error message
}
switch(choice){
case 1: //code
case 2: //code
.
.
.
case 7: //code
if (choice == 8) {
break; //will give flow control to next element after the while statement
}
}
}
回答by Anoop LL
You can give whole code(from displaying menu) inside a while loop and give condition as true so that after using a case it will automatically repeat(as you are using 6 to EXIT). And if any invalid input is given for eg:10 the case will go to default section and will execute the code there
您可以在 while 循环中提供整个代码（来自显示菜单）并将条件设为 true，以便在使用案例后它会自动重复（因为您使用 6 退出）。如果为 eg:10 提供任何无效输入，则案例将转到默认部分并在那里执行代码
import java.util.Scanner;
public class basicCalc {
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner input = new Scanner(System.in);
boolean mainLoop = true;
int choice;
while(true){
System.out.println("Calculator Main Menu\n");
System.out.print("1.) Addition \n");
System.out.print("2.) Subtraction.\n");
System.out.print("3.) Multiplication.\n");
System.out.print("4.) Division.\n");
System.out.print("5.) Generate Random Number.\n");
System.out.print("6.) Exit\n");
System.out.print("\nEnter Your Menu Choice: ");
choice = input.nextInt();
switch(choice){
case 1:
//Definitions
int adNumf, adNuml, sum;
System.out.print("Please Enter The First Number: ");
adNumf = input.nextInt();
System.out.print("\nPlease Enter The Second Number: ");
adNuml = input.nextInt();
sum = adNumf + adNuml;
System.out.print("The Sum Of Those Numbers is: " +sum);
break;
case 2:
int subNum1, subNum2, sum2;
System.out.println("\nPlease Enter The First Number: ");
subNum1 = input.nextInt();
System.out.println("Please Enter The Second Number: ");
subNum2 = input.nextInt();
sum2 = subNum1 - subNum2;
System.out.println("The Subtraction Leaves The Number: " +sum2);
break;
case 3:
int multNum1, multNum2, multTotal;
// Gather Input
System.out.println("Please Enter The First Number To Multiply: ");
multNum1 = input.nextInt();
System.out.println("Please Enter The Second Number To Multiply: ");
multNum2 = input.nextInt();
// This will Multiply the Numbers
multTotal = multNum1 * multNum2;
//Display Final
System.out.println("The Multiplied Numbers Are: " +multTotal);
break;
case 4:
//Definitions
double divNum1, divNum2, divTotal;
System.out.println("Enter Your Numerator ");
divNum1 = input.nextInt();
System.out.println("Enter Your Denominator ");
divNum2 = input.nextInt();
if(divNum2 == 0){
System.out.println("Zero is Not divisable, please select a new denominator: ");
divNum2 = input.nextInt();
}
divTotal = divNum1 / divNum2;
System.out.println("Your divisor is: " +divTotal);
break;
case 5:
double limL, limH, rand;
System.out.println("Enter Your Low Limit: ");
limL = input.nextInt();
System.out.println("Enter Your High Limit ");
limH = input.nextInt();
//Equation to keep numbers within bounds
rand = limL + (Math.random() * ((limH - limL) + 1));
System.out.println("Given Your Limits, the Random Number will be: " +rand);
break;
case 6:
System.out.println("Exiting Program...");
System.exit(0);
break;
default :
System.out.println("This is not a valid Menu Option! Please Select Another");
break;
}
}
}
}
回答by Daniel Stiefel
or try thisone
或者试试这个
import java.util.Scanner;
public class basicCalc {
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner input = new Scanner(System.in);
boolean mainLoop = true;
int choice;
do{
System.out.println("Calculator Main Menu\n");
System.out.print("1.) Addition \n");
System.out.print("2.) Subtraction.\n");
System.out.print("3.) Multiplication.\n");
System.out.print("4.) Division.\n");
System.out.print("5.) Generate Random Number.\n");
System.out.print("6.) Exit\n");
System.out.print("\nEnter Your Menu Choice: ");
choice = input.nextInt();
switch(choice){
case 1:
//do something
break;
case 2:
//do something
break;
case 3:
//do something
break;
case 4:
//do something
break;
case 5:
//do something
break;
case 6:
System.out.println("Exiting Program...");
System.exit(0);
break;
default:
System.out.println(choise + " is not a valid Menu Option! Please Select Another.");
}while(choice != 6 /*Exit loop when choice is 6*/);
}
}
