Using switch in Java but not sure why it works

I was trying to implement an option when my program starts to either enter the admin side or the storefront side. When I added using switch and case at the start of my program it worked right away but I don't know why. When I enter option 2 to go to the store front it enters and I thought I would need to make a method for it to enter the store front.

Can someone explain what is exactly happening at the beginning of my code? I think I just happened to get lucky.

	public static void main(String[] args) throws IOException {
while (true) {
System.out.println("Login to Admin site (1) or go to store front (2)?");
int choice = scnr.nextInt();
switch (choice) {
case 1:
StoreFront server = new StoreFront(0);
server.start(6666);
case 2:
}
inventoryManager.initializeInventoryFromFile("inventory.json");
System.out.println("Welcome to the Game Store \n");
System.out.println("Please select an option from the menu");
System.out.println("***************************************");
System.out.println("************MAIN MENU ******************\n");
while (true) {
System.out.println("Enter one of the following:\n\n" + "'1' : View Products\n" + "'2' : Purchase Products\n"
+ "'3' : Return Products\n" + "'4' : Exit");
int menuChoice = scnr.nextInt();
switch (menuChoice) {
case 1:
viewProducts();
break;
case 2:
purchaseProducts();
break;
case 3:
returnProducts();
break;
case 4:
System.out.println("Thank you for coming by. Please come again.");
System.exit(0);
break;
default:
System.out.println("INVALID OPTION. Please select an option 1-4");
scnr.close();
} 
//		server.cleanUp();
}
}
}	
}

> "... When I enter option 2 to go to the store front it enters and I thought I would need to make a method for it to enter the store front. ..."
>
> "... Can someone explain what is exactly happening at the beginning of my code? I think I just happened to get lucky."

No luck, that's how the switch structure will function.

It's an optimized equivalent of multiple if-else statements.

The following two structures are equivalent, in terms of control flow.
Note the break keyword.

switch (choice) {
    case 1:
        StoreFront server = new StoreFront(0);
        server.start(6666);
        break;
    case 2:
        break;
}

if (choice == 1) {
    StoreFront server = new StoreFront(0);
    server.start(6666);
} else if (choice == 2) {

}

Essentially, your second branch, case 2, has no attributing statements, so nothing is executed, and the switch is exited.

> "... is there a better way I could implement this? Would my way be "buggy" in a sense?"

It might be viewed as "buggy" since the branches don't require brackets, and forgetting to add the break keyword can cause the code to conflict.

It's a very old syntax, abstracted from the C programming language.
Similar to labels, which Java recommends to avoid unless necessary.

Here is an example of the newer switch structure, which has a slightly different syntax.

Instead of the colon, :, you use ->.  And, a break is inferred.

switch (choice) {
    case 1 -> {
        StoreFront server = new StoreFront(0);
        server.start(6666);
    }
    case 2 -> { }
}

</details>



# 答案2
**得分**: 0

你的示例中唯一的问题是这一部分：
```java
switch (choice) {
       case 1:
            StoreFront server = new StoreFront(0);
            server.start(6666);
                
       case 2:
}

在执行完 case 1 后，它会“穿透”到尚未定义的 case 2。除非你希望它们穿透，否则应在每个 case 后使用 break。

上述代码等同于：

if (choice == 1) {
     StoreFront server = new StoreFront(0);
     server.start(6666);
}
// 现在执行 case 2 应该做的事情

不要忘记 switch 表达式：

for (int choice : new int[]{2, 4}) {
    int result = switch (choice) {
        case 1, 2, 3 -> 5; // 对于 1、2 或 3 返回 5
        case 4, 5, 6 -> {  // 对于 4、5 或 6 也是类似的
            System.out.println("返回 6");
            yield 6;
        }
        default -> 1;
    };
    System.out.println("result = " + result);
}

打印结果为：

result = 5
返回 6
result = 6

switch (choice) {
case 1:
StoreFront server = new StoreFront(0);
server.start(6666);
case 2:
}

if(choice == 1) {
StoreFront server = new StoreFront(0);
server.start(6666);
}
// now execute what case 2 would do

for (int choice : new int[]{2,4}) {
int result = switch (choice) {
case 1, 2, 3 -> 5; // returns 5 for 1,2, or 3
case 4, 5, 6 -> {  // similar for 4,5,or 6
System.out.println("returning 6");
yield 6;
}
default -> 1;
};
System.out.println("result = " + result);
}

result = 5
returning 6
result = 6
</details>
# 答案3
**得分**: 0
你的第一个`switch`在下面的代码执行之前终止。如果你想让`case 2`执行下面的代码，那么代码必须在`case 2`的`body`内。
在`case 1`结束前添加`break`，以确保`case 2`不会执行。
```java
public static void main(String[] args) throws IOException {
while (true) {
System.out.println("登录到管理员网站（1）或进入商店前台（2）？");
int choice = scnr.nextInt();
switch (choice) {
case 1:
StoreFront server = new StoreFront(0);
server.start(6666);
break; // 在这里停止执行
case 2:
// 不要在这里关闭switch
inventoryManager.initializeInventoryFromFile("inventory.json");
System.out.println("欢迎来到游戏商店\n");
System.out.println("请选择菜单中的一个选项");
System.out.println("***************************************");
System.out.println("************主菜单 ******************\n");
while (true) {
System.out.println("输入以下选项之一：\n\n'1'：查看产品\n'2'：购买产品\n'3'：退货\n'4'：退出");
int menuChoice = scnr.nextInt();
switch (menuChoice) {
case 1:
viewProducts();
break;
case 2:
purchaseProducts();
break;
case 3:
returnProducts();
break;
case 4:
System.out.println("谢谢光临。请再次光临。");
System.exit(0);
break;
default:
System.out.println("无效选项。请选择1-4之间的选项");
scnr.close();
}
}
}
}
}

    public static void main(String[] args) throws IOException {
while (true) {
System.out.println("Login to Admin site (1) or go to store front (2)?");
int choice = scnr.nextInt();
switch (choice) {
case 1:
StoreFront server = new StoreFront(0);
server.start(6666);
break; //stops execution here
case 2:
//} //don't close switch here
inventoryManager.initializeInventoryFromFile("inventory.json");
System.out.println("Welcome to the Game Store \n");
System.out.println("Please select an option from the menu");
System.out.println("***************************************");
System.out.println("************MAIN MENU ******************\n");
while (true) {
System.out.println("Enter one of the following:\n\n" + "'1' : View Products\n" + "'2' : Purchase Products\n"
+ "'3' : Return Products\n" + "'4' : Exit");
int menuChoice = scnr.nextInt();
switch (menuChoice) {
case 1:
viewProducts();
break;
case 2:
purchaseProducts();
break;
case 3:
returnProducts();
break;
case 4:
System.out.println("Thank you for coming by. Please come again.");
System.exit(0);
break;
default:
System.out.println("INVALID OPTION. Please select an option 1-4");
scnr.close();
} 
//      server.cleanUp();
}//close switch here
}
}
}   
}