> For AI agents: the complete documentation index is available at https://nhanbe.id.vn/llms.txt, the full documentation bundle is available at https://nhanbe.id.vn/llms-full.txt.

# Adapter

## Overview

Convert the interface of a class into another interface clients expect.

## When to use

- You need to integrate a legacy or third-party API.
- You want to reuse existing classes without modifying them.

## Java example

```java
class LegacyLogger {
    void write(String msg) { /* ... */ }
}

interface Logger {
    void log(String msg);
}

class LegacyLoggerAdapter implements Logger {
    private final LegacyLogger legacy;
    LegacyLoggerAdapter(LegacyLogger legacy) { this.legacy = legacy; }
    public void log(String msg) { legacy.write(msg); }
}
```

## TypeScript example

```ts
class LegacyLogger {
  write(msg: string): void {}
}

interface Logger {
  log(msg: string): void;
}

class LegacyLoggerAdapter implements Logger {
  constructor(private legacy: LegacyLogger) {}
  log(msg: string): void {
    this.legacy.write(msg);
  }
}
```

## Pros and cons

Pros:

- Enables reuse without changing original code.
- Keeps client code stable.

Cons:

- Adds an extra abstraction layer.
- Too many adapters can complicate the codebase.

## Common pitfalls

- Over-adapting when a simpler wrapper works.
- Hiding breaking behavior differences.

## Related patterns

- [Facade](https://nhanbe.id.vn/design-patterns/structural/facade.md)
- [Bridge](https://nhanbe.id.vn/design-patterns/structural/bridge.md)