What are the characteristics of TreeMap in java

Explanation

1. The bottom layer of TreeMap uses a red-black tree, and the key values ​​stored in TreeMap are sorted by key.

2. If the Key is stored in a string or other types, it will be sorted according to the default order of the dictionary.

If you import a custom reference type, such as User, the object must implement the Comparable interface and override its compareTo method; or when creating a TreeMap, you must specify the comparator used.

Example

// 方式一：定义该类的时候，就指定比较规则
class User implements Comparable{
    @Override
    public int compareTo(Object o) {
        // 在这里边定义其比较规则
        return 0;
    }
}
public static void main(String[] args) {
    // 方式二：创建TreeMap的时候，可以指定比较规则
    new TreeMap<User, Integer>(new Comparator<User>() {
        @Override
        public int compare(User o1, User o2) {
            // 在这里边定义其比较规则
            return 0;
        }
    });
}

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