"Not tired yet? Let's carry on, then. I'd like to give you more details about Set and Map and what they can do."

"**Set** is a set, a group of unnumbered objects. The main feature of a Set is that it only contains unique objects, i.e. each element of the set is different. Here are operations you can perform on a set:"

Operation | Method |
---|---|

Add element(s) | add(), addAll() |

Remove element(s) | remove(), removeAll() |

Check for the presence of element(s) | contains(), containsAll() |

"And that's it?"

"Well, yes. You can also use the size() method to find out how many elements are in the set."

"What about Map?"

"**Map** is a set of pairs. It's like a Set, except it's a set of key-value pairs rather than unique elements. The only limitation is that each «key» must be unique. A Map can't contain two pairs with the same keys."

"Here's what we can do with **Map**:"

Operation | Method |
---|---|

Get a set of all pairs | entrySet() |

Get a set of all keys | keySet() |

Get a set of all values | values() |

Add a pair | put(key, value) |

Get the value for the specified key | get(key) |

Check whether the specified key is present | containsKey(key) |

Check whether the specified value is present | containsValue(value) |

Check whether the Map is empty | isEmpty() |

Clear the Map | clear() |

Remove the value for the specified key | remove(key) |

"This is much more interesting than Set."

"Yes. Although Map isn't as popular as List, it is used in many tasks."

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