Explain the difference between routing, forwarding, and switching.用中文解释

路由、转发和交换的区别在于它们所处理的网络层级不同。路由是对大规模网络不同部分之间的数据包进行转移的过程，是在网络层中实现的；转发是将从源端传来的数据包当场向目的网络接口进行发送的过程，是在数据链路层中实现的；交换则是在物理层和数据链路层中实现的，它是将数据包从一个接口直接发送到另一个接口，无需传递到网络层。简单来说，路由用于连接多个网络；转发用于在同一个网络中传递数据；交换用于在同一个局域网中传递数据。

相关问题

2)Explain the difference between State pattern and Decorator pattern.5)Give the code required for the classes introduced in question 2), focusing on the code for a method selectState() which changes the value that is being adjusted from years to months. Make it clear in which classes the code is to be found. Assume the existence of other methods that are needed such as getMonthSetUpState().

2) The State pattern is a behavioral design pattern that allows an object to alter its behavior when its internal state changes. This pattern involves creating state objects that represent various states of the object and a context object whose behavior varies as its state object changes.

On the other hand, the Decorator pattern is a structural design pattern that allows behavior to be added to an individual object, either statically or dynamically, without affecting the behavior of other objects from the same class. This pattern involves creating decorator objects that wrap the original object and provide additional functionality while keeping the original object's interface intact.

5) Here is the code for the classes introduced in question 2), focusing on the code for a method selectState() which changes the value that is being adjusted from years to months:

// Context interface
interface Account {
    void selectState(State state);
    void deposit(double amount);
    void withdraw(double amount);
    double getBalance();
}

// Concrete Context class
class SavingsAccount implements Account {
    private State state;
    private double balance;
    
    public SavingsAccount() {
        this.state = new YearsSetUpState(); // default state
        this.balance = 0.0;
    }
    
    @Override
    public void selectState(State state) {
        this.state = state;
    }
    
    @Override
    public void deposit(double amount) {
        this.balance += state.adjustDeposit(amount);
    }
    
    @Override
    public void withdraw(double amount) {
        this.balance -= state.adjustWithdrawal(amount);
    }
    
    @Override
    public double getBalance() {
        return this.balance;
    }
    
    // Other methods needed
    public State getMonthSetUpState() {
        return new MonthsSetUpState();
    }
}

// State interface
interface State {
    double adjustDeposit(double deposit);
    double adjustWithdrawal(double withdrawal);
}

// Concrete State classes
class YearsSetUpState implements State {
    @Override
    public double adjustDeposit(double deposit) {
        return deposit;
    }
    
    @Override
    public double adjustWithdrawal(double withdrawal) {
        return withdrawal;
    }
}

class MonthsSetUpState implements State {
    @Override
    public double adjustDeposit(double deposit) {
        return deposit / 12;
    }
    
    @Override
    public double adjustWithdrawal(double withdrawal) {
        return withdrawal / 12;
    }
}

In the above code, the `Account` interface represents the context object, while the `State` interface represents the state objects. The `SavingsAccount` class is a concrete context class that implements the `Account` interface and keeps track of the current state object. The `YearsSetUpState` and `MonthsSetUpState` classes are concrete state classes that implement the `State` interface and provide specific behavior for each state.

The `selectState()` method is implemented in the `SavingsAccount` class and allows the current state object to be changed. The `deposit()` and `withdraw()` methods use the current state object to adjust the deposit and withdrawal amounts accordingly. The `getBalance()` method returns the current balance of the account.

The `getMonthSetUpState()` method is also implemented in the `SavingsAccount` class and returns a new `MonthsSetUpState` object, which can be used to change the current state object to adjust the deposit and withdrawal amounts from years to months.

1.Explain how bytecode (either CIL or Java bytecode) differs from machine code with examples of instructions. 2.Why autoboxing and autounboxing is not needed in C#? 3.How to decide when and when not to use auto-implemented properties in C#? 4.What is the difference between structs and class in C#? 5.How to decide between using a regular parameter declaration and a ref parameter declaration in a C# method? 6.What is the difference between modifiers new and override in C#? 7.How to decide between using a two-dimensional array and an array of arrays in a programming situation in C#? 8.Discuss the common errors that can arise with switch statements in Java and how C# eliminates those errors automatically. 9.How to use foreach loop in C#? Give one example. 10.What does this program print on the screen? Explain your answer by describing what a delegate is, including the meaning of +=. class C { delegate bool Check (int number); static bool IsEven (int number) { return number % 2 == 0;} static bool IsSmallerThan3 (int number) { return number < 3;} static void Main () { Check f = IsEven; f += IsSmallerThan3; Console.WriteLine ( f(3)); Console.WriteLine ( f(2)); } }

1. Bytecode is an intermediate code that is generated by a compiler to be executed by a virtual machine. It is platform-independent and can be executed on any platform that has a virtual machine installed. Machine code, on the other hand, is the binary code that is directly executed by a computer's CPU. Here are some examples of instructions in bytecode and machine code:

- Bytecode (CIL): ldloc.0 (load local variable 0), ldc.i4.5 (load constant value 5), add (addition)
- Machine code: mov eax, [ebp-4] (move value from memory to register), mov ebx, 5 (move constant value to register), add eax, ebx (addition)

2. Autoboxing and autounboxing is not needed in C# because C# has a feature called "value types" that allows the value types to be treated like objects. This means that value types can be used in collections and passed as parameters to methods without the need for autoboxing and autounboxing.

3. Auto-implemented properties should be used when there is no additional logic required for the getter or setter methods. If additional logic is required, then a regular property with custom getter or setter methods should be used.

4. Structs and classes are similar in that they both can contain fields, methods, and properties. The main difference is that structs are value types, while classes are reference types. This means that structs are passed by value, while classes are passed by reference.

5. A regular parameter declaration should be used when the method only needs to read the value of the parameter. A ref parameter declaration should be used when the method needs to modify the value of the parameter.

6. The "new" modifier is used to hide a method or property in a derived class, while the "override" modifier is used to replace a method or property in a base class with a new implementation in a derived class.

7. A two-dimensional array should be used when the data is logically a matrix or a table with rows and columns. An array of arrays should be used when the data is logically a collection of arrays.

8. In Java, the switch statement can cause errors if there are duplicate case values or if the break statement is not used after each case. In C#, the switch statement automatically eliminates these errors by requiring a default case and not allowing fall-through cases.

9. The foreach loop is used to iterate over a collection of items, such as an array or a list. Here is an example:

int[] numbers = { 1, 2, 3, 4, 5 };
foreach (int number in numbers)
{
    Console.WriteLine(number);
}

10. The program will print "True" and "False" because the delegate "f" contains two methods, "IsEven" and "IsSmallerThan3", which are both called when "f" is invoked with a parameter. The "+=" operator is used to add the "IsSmallerThan3" method to the delegate "f". A delegate is a type that encapsulates a method or a group of methods, and the "+=" operator is used to add a method to a delegate's invocation list.