Thread priority in Java is a hint to the thread scheduler about the relative importance of a thread compared to others. Each thread has an integer priority that helps determine the order in which threads are scheduled for execution. Although the scheduler behavior is platform-dependent and not guaranteed, thread priority can influence which thread is more likely to be executed sooner when multiple threads are waiting for CPU time.

Key Concepts and Priority Levels

• Priority Range: Java thread priorities range from 1 (lowest) to 10 (highest).

• Default Priority: Threads by default have a priority of 5, represented by Thread.NORM_PRIORITY.

• Minimum and Maximum Priorities:

  • Thread.MIN_PRIORITY is 1.
  • Thread.MAX_PRIORITY is 10.

• Setting and Getting Priority:

  • Use setPriority(int newPriority) to set a thread's priority.
  • Use getPriority() to retrieve a thread's current priority.

Below is a summary table of thread priorities:

Why Thread Priority Matters

• Influence on Scheduling: Threads with higher priority are generally more likely to be chosen by the scheduler for execution. However, priority is only a suggestion to the scheduler; it does not guarantee execution order.
• Use Cases: Useful in scenarios where some tasks are more critical than others (e.g., user interface responsiveness vs. background data processing).
• Caution: Overusing thread priorities can lead to issues like starvation, where lower-priority threads never get CPU time.

Example: Setting Thread Priorities

This example creates two threads with different priorities. One thread is given the maximum priority, and the other the minimum. The code prints each thread's name, priority, and a counter to illustrate how priorities are set.

Example Explanation:

• Thread Creation and Priority Setting:
  • Two custom threads (Thread-1 and Thread-2) are created.
  • Thread-1 is assigned the maximum priority (10) using setPriority(Thread.MAX_PRIORITY).
  • Thread-2 is assigned the minimum priority (1) using setPriority(Thread.MIN_PRIORITY).
• Execution Flow:
  • The threads are started concurrently with start().
  • Each thread prints its name, current priority, and a count from 1 to 5.
  • The Thread.sleep(500) call pauses each thread for 0.5 seconds between counts, allowing for observable interleaving.
• Impact of Priority:
  • Although higher priority suggests that Thread-1 may run more frequently, exact scheduling is managed by the JVM and may vary by system.

Thread priority in Java provides a mechanism to hint the scheduler about the relative importance of threads. With priorities ranging from 1 (minimum) to 10 (maximum), you can influence which threads are more likely to be executed sooner. Although thread priority is not a guarantee and is platform-dependent, it is a useful tool for managing thread execution in concurrent applications.