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What impact will the addition of the static keyword when declaring ConcurrentHashMap in Java?
What impact will the addition of the static keyword when declaring ConcurrentHashMap in Java?
Apr 19, 2025 pm 03:51 PM
Impact of static keywords in Java ConcurrentHashMap declaration
ConcurrentHashMap is an efficient concurrent hash table used in Java for multi-threaded environments, ensuring performance and thread safety during multi-threaded concurrent read and write. This article explores the impact of adding static keywords when declaring ConcurrentHashMap .
ConcurrentHashMap Overview
ConcurrentHashMap is a thread-safe hash table that stores key-value pairs. It allows multiple threads to read and write concurrently and maintain high performance through segment locking (JDK 1.7 and previous versions) or an optimized concurrency control mechanism (JDK 1.8 and later versions). JDK 1.8 and later abandoned segmented locks, used CAS and synchronized to ensure thread safety, and used red and black trees to handle hash conflicts.
ConcurrentHashMap is mainly used in scenarios where multiple threads need to access the same hash table, reducing lock competition, and improving concurrency performance. It is a thread-safe alternative to HashMap .
Example of usage
The following example demonstrates the use of ConcurrentHashMap :
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
public class ConcurrentHashMapExample {
public static void main(String[] args) throws InterruptedException {
ConcurrentHashMap<string integer> map = new ConcurrentHashMap(); // Instance variable ExecutorService executor = Executors.newFixedThreadPool(10);
for (int i = 0; i {
map.put("key" taskNumber, taskNumber);
System.out.println("Task " taskNumber " put value: " map.get("key" taskNumber));
});
}
executor.shutdown();
executor.awaitTermination(1, TimeUnit.MINUTES);
}
}</string>
In this example, ConcurrentHashMap is created as an instance variable, and each thread updates it concurrently. Due to its thread-safe nature, the program can run correctly.
Impact of static keyword
The effect of adding static keywords in ConcurrentHashMap declaration depends on its scope:
Add
static:ConcurrentHashMapbecomes a class variable with a global life cycle, which exists throughout the application life cycle, and all class instances are shared. This is suitable for scenarios where the sameConcurrentHashMapis needed to share between multiple methods or instances. However, usingstaticvariables requires caution, as incorrect modifications can affect the entire application.Don't add
static:ConcurrentHashMapbecomes an instance variable, with the same life cycle as the object that created it. When the object is destroyed,ConcurrentHashMapis also destroyed and will not affect other instances. This is suitable for scenarios whereConcurrentHashMapis used internally in an object.
Choosing whether to use static depends on the specific business needs. Normally, it is not recommended to use static to modify ConcurrentHashMap unless there is a clear sharing requirement to avoid potential concurrency problems and code maintenance complexity. Prefer instance variables to improve code readability and maintainability.
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