# 桥接模式

   **桥接模式(Bridge Pattern)：** 将抽象部分与它的具体实现部分分离，使它们都可以独立地变化。它是一种对象结构型模式，又称为柄体(Handle and Body)模式或接口(Interface)模式。通过组合的方式实现两个类之间联系，而不是继承。

## 适用场景

* 抽象和具体实现之间增加更多的灵活性
* 一个类存在两个（或者多个）独立变化的维度，并且这两个（或者多个）维度都需要独立进行扩展
* 不希望使用继承，或者因为多层继承导致系统类的个数剧增

## 优点

* 分离抽象部分及其具体实现部分
* 提高了系统的可扩展性
* 符合开闭原则
* 符合合成复用原则

## 缺点

* 增加了系统的理解与设计难度
* 需要正确地识别出系统中两个独立变化的维度

下面我们引入一种应用场景，银行有很多种，每种银行又可以又多种储蓄账户，例如活期和定期。

## Golang Demo

```go
package bridge

// 账户
type Account interface {
    openAccount() Account
    showAccountType()
}
```

```go
package bridge

type Bank interface {
    openAccount() Account
}
```

```go
package bridge

import "fmt"

type DepositAccount struct {
}

func NewDepositAccount() *DepositAccount {
    return &DepositAccount{}
}

func (DepositAccount) openAccount() Account {
    fmt.Println("打开定期账号")
    return *NewDepositAccount()
}

func (DepositAccount) showAccountType() {
    fmt.Println("这是一个定期账号")
}
```

```go
package bridge

import "fmt"

type SavingAccount struct {
}

func NewSavingAccount() *SavingAccount {
    return &SavingAccount{}
}

func (SavingAccount) openAccount() Account {
    fmt.Println("打开活期账号")
    return *NewSavingAccount()
}

func (SavingAccount) showAccountType() {
    fmt.Println("这是一个活期账号")
}
```

```go
package bridge

import "fmt"

type ABCBank struct {
    account Account
}

func NewABCBank(account Account) *ABCBank {

    return &ABCBank{account: account}
}

func (abc ABCBank) openAccount() Account {
    fmt.Println("打开中国农业银行账号")
    abc.account.openAccount()
    return abc.account
}
```

```go
package bridge

import "fmt"

type ICBCBank struct {
    account Account
}

func NewICBCBank(account Account) *ICBCBank {

    return &ICBCBank{account: account}
}

func (icbc ICBCBank) openAccount() Account {

    fmt.Println("打开中国工商银行账号")
    icbc.account.openAccount()
    return icbc.account
}
```

```go
package bridge

import "testing"

func Test(t *testing.T) {
    var icbcBank Bank = NewICBCBank(NewDepositAccount())
    icbcAccount := icbcBank.openAccount()
    icbcAccount.showAccountType()

    var abcBank Bank = NewABCBank(NewSavingAccount())
    abcAccount := abcBank.openAccount()
    abcAccount.showAccountType()
}
```

## Java Demo

定义一个接口，里面定义了两种账户。

```java
package tech.selinux.design.pattern.structural.bridge;

public interface Account {
  Account openAccount();

  void showAccountType();
}
```

定义一个抽象类的银行，里面有一个账户，同时有一个与账户同名的方法。

```java
package tech.selinux.design.pattern.structural.bridge;

public abstract class Bank {
  protected Account account;

  public Bank(Account account) {
    this.account = account;
  }

  abstract Account openAccount();
}
```

分别定义两种账户的实现类。

```java
package tech.selinux.design.pattern.structural.bridge;

public class DepositAccount implements Account {
  @Override
  public Account openAccount() {
    System.out.println("打开定期账号");
    return new DepositAccount();
  }

  @Override
  public void showAccountType() {
    System.out.println("这是一个定期账号");
  }
}
```

```java
package tech.selinux.design.pattern.structural.bridge;

public class SavingAccount implements Account {
  @Override
  public Account openAccount() {
    System.out.println("打开活期账号");
    // ...
    return new SavingAccount();
  }

  @Override
  public void showAccountType() {
    System.out.println("这是一个活期账号");
  }
}
```

接下来定义两种银行的实现类。

```java
package tech.selinux.design.pattern.structural.bridge;

public class ABCBank extends Bank {
  public ABCBank(Account account) {
    super(account);
  }

  @Override
  Account openAccount() {
    System.out.println("打开中国农业银行账号");
    account.openAccount();
    return account;
  }
}
```

```java
package tech.selinux.design.pattern.structural.bridge;

public class ICBCBank extends Bank {
  public ICBCBank(Account account) {
    super(account);
  }

  @Override
  Account openAccount() {
    System.out.println("打开中国工商银行账号");
    account.openAccount();
    return account;
  }
}
```

然后我们来进行一下测试。

```java
package tech.selinux.design.pattern.structural.bridge;

public class Test {
  public static void main(String[] args) {
    Bank icbcBank = new ICBCBank(new DepositAccount());
    Account icbcAccount = icbcBank.openAccount();
    icbcAccount.showAccountType();

    Bank icbcBank2 = new ICBCBank(new SavingAccount());
    Account icbcAccount2 = icbcBank2.openAccount();
    icbcAccount2.showAccountType();

    Bank abcBank = new ABCBank(new SavingAccount());
    Account abcAccount = abcBank.openAccount();
    abcAccount.showAccountType();
  }
}
```

## UML

![桥接模式UML](/files/-LdObIL6cgEDE-x5fTsB)

### 补充另一个版本的Java/Scala Demo 以及源码解析

## Java Demo\_

## Scala Demo

## UML\_

## 源码解析


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://www.selinux.tech/designpattern/structural-pattern/bridge-pattern.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.