December 7, 2023

How to get the environment variables in Java

In Java, the System.getenv() returns an unmodifiable string Map view of the current system environment. If a requested environment variable is not defined, the System.getenv will return a null, and with Java 8 uses Optional to handle the null. The System.getenv() returns an unmodifiable string Map, modify the Map will cause UnsupportedOperationException.

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How to sort a Map in Java

Few Java examples to sort a Map by its keys or values: (1) Uses java.util.TreeMap, it will sort the Map by keys automatically, (2) Yet another java.util.TreeMap example, provide a custom Comparator to sort the key in descending order, (3) Sort by Value – Converts the Map into a List, sorts the List with a custom Comparator and put it into a new insertion order map – LinkedHashMap

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