Advanced skills of Java Map: Master cold knowledge you may not know and improve your programming skills

php editor Baicao will take you to explore the advanced techniques of Java Map, reveal the cold knowledge that may be ignored, and help you improve your programming skills. Map is one of the commonly used data structures in Java. An in-depth understanding of its advanced usage will help optimize code logic and improve program efficiency. It will also make you more comfortable in the programming field. Let us uncover the mystery of Java Map together and open up a new realm of programming skills!

The Map interface is a data structure used to store key-value pairs in the Java collection framework . It allows you to use keys to find and retrieve associated values. The Map interface provides many useful methods, including put(), get(), remove(), containsKey(), containsValue(), size(), isEmpty(), etc.

Implementation of Map

The most commonly used Map implementations in Java are HashMap and TreeMap. HashMap is a hash table-based Map implementation that quickly finds and retrieves values ​​by computing hashes of keys. TreeMap is a Map implementation based on a red-black tree that sorts the keys in ascending or descending order.

Map.Entry

Map.Entry interface represents key-value pairs in Map. It provides some useful methods, including geTKEy(), getValue(), setValue(), etc. You can use Map.Entry to iterate over key-value pairs in a Map.

forEach() and lambda expressions

Java 8 introduced the forEach() method and lambda expressions, which make traversing Map easier and more concise. You can use the forEach() method and lambda expressions to iterate over the key-value pairs in a Map and perform specific operations on each key-value pair.

Common usage of Map

Map has a wide range of applications in Java, including:

• Cache data: Map can be used to cache frequently accessed data to improve application performance.
• Configuration information: Map can be used to store the configuration information of the application, such as DatabaseConnectionString, Serveraddress, etc. .
• Associated data: Map can be used to store associated data, such as the association between a student and his course grades.
• Object attributes: Map can be used to store the attributes of an object, such as a person's name, age, address, etc.

Advanced Map Tips

In addition to basic usage, Map also provides many advanced techniques that can help you improve programming efficiency and solve complex problems. Here are some commonly used advanced techniques:

• Using a custom comparator: You can use a custom comparator to sort keys in a Map. For example, if you want to sort the keys in a Map in descending order, you can use the following code:

Map<String, Integer> map = new TreeMap<>(Collections.reverseOrder());

• Use null keys and values: Map allows you to use null keys and values. However, you should use null keys and values ​​with caution as they may cause unexpected behavior.
• Using Map.EntrySet(): The Map.EntrySet() method returns a collection of all key-value pairs in the Map. You can use Map.EntrySet() to iterate over key-value pairs in a Map.
• Use Map.keySet() and Map.values(): The Map.keySet() method returns the set of all keys in the Map, while the Map.values() method returns the set of all the values ​​in the Map . You can use Map.keySet() and Map.values() to iterate over the keys and values ​​in a Map.

Summarize

Java Map is a powerful data structure that provides many useful methods and techniques. By mastering these advanced techniques, you can improve your programming efficiency and solve complex problems.

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