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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.