Programação de Threads em Java

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THREAD 
PROGRAMMING IN 
JAVA
Prof. Dr. Everton Cavalcante
https://www.docente.ufrn.br/everton.cavalcante
https://www.docente.ufrn.br/everton.cavalcante
IDEAL INTERFACE FOR THREAD PROGRAMMING
• Creation
• Termination
• Wait
• Identifier retrieval
• Identifier comparison
• Access/modification of attributes
2
GOALS
To introduce concurrent programming using 
threads in the Java programming language
3
THREADS IN JAVA
• Every Java program has at least one thread
o main(String) – main method
o It is terminated when all statements within the main method and other 
ones called by it are executed
• Java includes multithreading primitives as part of the language
o Portability
• Other threads can be created besides the main thread
o Write the code to be executed by the thread
o Write the code to create and run the thread
4
THE LIFE CYCLE OF THREADS IN JAVA
new
running
wait time wait terminated
program starts 
the thread
ti
m
e
 e
xp
ir
es
5
CREATING THREADS (1/3)
public class 
extends java.lang.Thread
implements java.lang.Runnable
6
CREATING THREADS (2/3)
Extending the java.lang.Thread class
• Instantiation of an object of the class derived from Thread
• Overriding of the run method inherited from the Thread superclass
o Coding the statements to be executed
• Invocation of the start method inherited from the Thread superclass to run 
the thread
o This method must not be overridden by the derived class
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CREATING THREADS (3/3)
Implementing the java.lang.Runnable interface
• Mandatory implementation of the run method defined by Runnable
o Coding the statements to be executed
o Coding a class that implements the Runnable interface promotes separation between the 
main program and the task to be executed
• Instantiation of an object of the derived class
• Instantiation of an object of the Thread class by providing the created 
Runnable object as a parameter to its constructor
• Invocation of the start method to run the thread
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IMPORTANT METHODS FOR JAVA 
MULTITHREADING (1/3)
Method Description
sleep Make the thread to wait
join Make the thread to wait the termination of another thread
currentThread Return a reference to the running thread
getId Return the thread’s unique identifier
getName Return the name of the thread
isAlive Check if the thread is running
getPriority Return the thread’s priority level
setPriority Modify the thread’s priority level
getState Return the thread state
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IMPORTANT METHODS FOR JAVA 
MULTITHREADING
.sleep
t1
t2
running state wait state
t2.start()
t1.sleep()
t1.run()
t2.run()
t1 resumes executiont1.start()
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IMPORTANT METHODS FOR JAVA 
MULTITHREADING (3/3)
For the sake of consistency, methods that abruptly interrupt the 
execution of a thread have been deprecated since JDK 1.2
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THREAD PRIORITY
Java allows assigning individual priorities to threads towards 
driving the scheduler to decide which threads should run
• MAX_PRIORITY
• MIN_PRIORITY
• NORM_PRIORITY
Integer constants defined in 
the java.lang.Thread class
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CHECK IT OUT
Code on GitHub
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https://github.com/ufrn-concprog/java-threads-examples/
SOME USEFUL TIPS
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SOME USEFUL TIPS (1/9)
Thread Magic Tricks: 5 Things You Never Knew 
You Can Do with Java Threads
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https://www.harness.io/blog/5-things-you-can-do-with-java-threads
https://www.harness.io/blog/5-things-you-can-do-with-java-threads
SOME USEFUL TIPS (2/9)
1. Naming threads eases debugging
…through parameterized constructor
public class Worker extends Thread {
 public Worker(String name) {
 super(name);
 }
 @Override
 public void run() {
// Thread's tasks
 }
}
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SOME USEFUL TIPS (3/9)
1. Naming threads eases debugging
…through a setter method
public class Worker extends Thread {
 protected String name;
 public void setThreadName(String name) {
 this.name = name;
 }
 @Override
 public void run() {
 // Thread's tasks
 }
}
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SOME USEFUL TIPS (4/9)
2. To wisely use priorities
• Despite Java programs being portable, priorities are handled in distinct ways 
according to the operating system
o Each Java thread opens a new native thread on the operating system level, and the Java 
priorities set are translated to native priorities in a different way for each platform
o Priorities can be viewed as recommendations to the operating system’s scheduler
o The -XX:+UseThreadPriorities flag must be included when running the program to 
consider the priorities
• Using thread priorities in an indiscriminate way may lead them to a 
starvation condition
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SOME USEFUL TIPS (5/9)
3. To use threads to execute tasks in background
• Threads as daemons can execute non-critical tasks in background
• Java allows checking and specifying if a thread is a daemon
o isDaemon and setDaemon methods
• As threads inherit the status of their respective parent threads, 
a daemon thread can create other threads as daemons
19
SOME USEFUL TIPS (6/9)
4. To have fine-grained control of the execution of threads over the 
processor (a.k.a. processor affinity)
• Processor affinity allows to specify over which processor a given thread will 
be executed
o This is defined by the operating system’s scheduler in conjunction with the Java Virtual 
Machine (JVM), considering thread priorities
• An interesting case when a thread can use cache and hence have the 
required data in a faster way
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SOME USEFUL TIPS (7/9)
4. To have fine-grained control of the execution of threads over the 
processor (a.k.a. processor affinity)
• Linux: command taskset –c 
• Java does not provide processor affinity mechanisms
o Thread Affinity is a third-party library that allows binding a thread to a given core
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https://github.com/OpenHFT/Java-Thread-Affinity
SOME USEFUL TIPS (8/9)
5. To use the Java SE Monitoring and Management facilities to 
monitor the execution of threads, either programmatically via 
the java.lang.management package or using the JConsole tool
• Number of classes loaded and threads running
• Thread state, statistics, and stack trace
• Memory and CPU usage
• Deadlock detection
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https://docs.oracle.com/en/java/javase/23/management/overview-java-se-monitoring-and-management.html
https://docs.oracle.com/en/java/javase/23/docs/api/java.management/java/lang/management/package-summary.html
https://docs.oracle.com/en/java/javase/23/management/using-jconsole.html
SOME USEFUL TIPS (9/9)
Using the JConsole tool
23
https://docs.oracle.com/en/java/javase/23/management/using-jconsole.html
THREAD 
PROGRAMMING IN 
JAVA
Prof. Dr. Everton Cavalcante
https://www.docente.ufrn.br/everton.cavalcante
https://www.docente.ufrn.br/everton.cavalcante
	Slide 1: THREAD PROGRAMMING IN JAVA
	Slide 2: Ideal interface for thread programming
	Slide 3: GOALS
	Slide 4: THREADS IN JAVA
	Slide 5: THE LIFE CYCLE OF THREADS IN JAVA
	Slide 6: CREATING THREADS (1/3)
	Slide 7: CREATING THREADS (2/3)
	Slide 8: CREATING THREADS (3/3)
	Slide 9: Important methods for Java multithreading (1/3)
	Slide 10: Important methods for Java multithreading
	Slide 11: Important methods for Java multithreading (3/3)
	Slide 12: THREAD PRIORITY
	Slide 13: CHECK IT OUT
	Slide 14: SOME USEFUL TIPS
	Slide 15: SOME USEFUL TIPS (1/9)
	Slide 16: SOME USEFUL TIPS (2/9)
	Slide 17: SOME USEFUL TIPS (3/9)
	Slide 18: SOME USEFUL TIPS (4/9)
	Slide 19: SOME USEFUL TIPS (5/9)
	Slide 20: SOME USEFUL TIPS (6/9)
	Slide 21: SOME USEFUL TIPS (7/9)
	Slide 22: SOME USEFUL TIPS (8/9)
	Slide 23: SOME USEFUL TIPS (9/9)
	Slide 24: THREAD PROGRAMMING IN JAVA