只允许在接口中使用某一组字符串作为键

enum AllowedKeys {
  KEY1("key1"),
  KEY2("key2"),
  KEY3("key3");

  private final String value;

  AllowedKeys(String value) {
    this.value = value;
  }

  public String getValue() {
    return value;
  }
}

public interface MyInterface {
  void setValue(AllowedKeys key, String value);
  String getValue(AllowedKeys key);
}

public class MyClass implements MyInterface {
  private Map<AllowedKeys, String> map = new HashMap<>();

  @Override
  public void setValue(AllowedKeys key, String value) {
    map.put(key, value);
  }

  @Override
  public String getValue(AllowedKeys key) {
    return map.get(key);
  }
}