#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

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

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
• Bridge