Multithreading in java is a process of executing multiple threads simultaneously. Thread is basically a lightweight sub-process, a smallest unit of processing. Thread is executed inside the process.
With multithreading threads share a common memory area. Java Multithreading is mostly used in games, animation etc. There is context-switching between the threads. There can be multiple processes inside the OS and one process can have multiple threads.
A thread can be in one of the five states. According to sun, there is only 4 states in thread life cycle in java new, runnable, non-runnable and terminated. There is no running state. But for better understanding the threads, we are explaining it in the 5 states.
The life cycle of the thread in java is controlled by JVM.
How to create thread: There are two ways to create a thread:
Thread class:
Thread class provide constructors and methods to create and perform operations on a thread.Thread class extends Object class and implements Runnable interface.
Runnable interface:
The Runnable interface should be implemented by any class whose instances are intended to be executed by a thread. Runnable interface have only one method named run().
public void run(): is used to perform action for a thread.
Starting a thread:
start() method of Thread class is used to start a newly created thread. It performs following tasks:
A new thread starts(with new callstack).
The thread moves from New state to the Runnable state.
When the thread gets a chance to execute, its target run() method will run.
1) Java Thread Example by extending Thread class
class Multi extends Thread{
public void run(){
System.out.println("thread is running...");
}
public static void main(String args[]){
Multi t1=new Multi();
t1.start();
}
}
Output:thread is running...
2) Java Thread Example by implementing Runnable interface
class Multi3 implements Runnable{
public void run(){
System.out.println("thread is running...");
}
public static void main(String args[]){
Multi3 m1=new Multi3();
Thread t1 =new Thread(m1);
t1.start();
}
}
Output:thread is running...
Sleep method in java
The sleep() method of Thread class is used to sleep a thread for the specified amount of time.
Syntax of sleep() method in java
The Thread class provides two methods for sleeping a thread:
public static void sleep(long miliseconds)throws InterruptedException
public static void sleep(long miliseconds, int nanos)throws InterruptedException
Example of sleep method in java
class TestSleepMethod1 extends Thread{
public void run(){
for(int i=1;i<5;i++){
try{Thread.sleep(500);}catch(InterruptedException e){System.out.println(e);}
System.out.println(i);
}
}
public static void main(String args[]){
TestSleepMethod1 t1=new TestSleepMethod1();
TestSleepMethod1 t2=new TestSleepMethod1();
t1.start();
t2.start();
}
}
The join() method
The join() method waits for a thread to die. In other words, it causes the currently running threads to stop executing until the thread it joins with completes its task.
Syntax:
public void join()throws InterruptedException
public void join(long milliseconds)throws InterruptedException
Example of join() method
class TestJoinMethod1 extends Thread{
public void run(){
for(int i=1;i<=5;i++){
try{
Thread.sleep(500);
}catch(Exception e){System.out.println(e);}
System.out.println(i);
}
}
public static void main(String args[]){
TestJoinMethod1 t1=new TestJoinMethod1();
TestJoinMethod1 t2=new TestJoinMethod1();
TestJoinMethod1 t3=new TestJoinMethod1();
t1.start();
try{
t1.join();
}catch(Exception e){System.out.println(e);}
t2.start();
t3.start();
}
}
Priority of a Thread (Thread Priority):
Each thread have a priority. Priorities are represented by a number between 1 and 10. In most cases, thread schedular schedules the threads according to their priority (known as preemptive scheduling). But it is not guaranteed because it depends on JVM specification that which scheduling it chooses.
3 constants defiend in Thread class:
public static int MIN_PRIORITY
public static int NORM_PRIORITY
public static int MAX_PRIORITY
Default priority of a thread is 5 (NORM_PRIORITY). The value of MIN_PRIORITY is 1 and the value of MAX_PRIORITY is 10.
Example of priority of a Thread:
class TestMultiPriority1 extends Thread{
public void run(){
System.out.println("running thread name is:"+Thread.currentThread().getName());
System.out.println("running thread priority is:"+Thread.currentThread().getPriority());
}
public static void main(String args[]){
TestMultiPriority1 m1=new TestMultiPriority1();
TestMultiPriority1 m2=new TestMultiPriority1();
m1.setPriority(Thread.MIN_PRIORITY);
m2.setPriority(Thread.MAX_PRIORITY);
m1.start();
m2.start();
}
}
Daemon Thread in Java
Daemon thread in java is a service provider thread that provides services to the user thread. Its life depend on the mercy of user threads i.e. when all the user threads dies, JVM terminates this thread automatically.
There are many java daemon threads running automatically e.g. gc, finalizer etc.
You can see all the detail by typing the jconsole in the command prompt. The jconsole tool provides information about the loaded classes, memory usage, running threads etc.
Points to remember for Daemon Thread in Java
It provides services to user threads for background supporting tasks. It has no role in life than to serve user threads.
With multithreading threads share a common memory area. Java Multithreading is mostly used in games, animation etc. There is context-switching between the threads. There can be multiple processes inside the OS and one process can have multiple threads.
A thread can be in one of the five states. According to sun, there is only 4 states in thread life cycle in java new, runnable, non-runnable and terminated. There is no running state. But for better understanding the threads, we are explaining it in the 5 states.
The life cycle of the thread in java is controlled by JVM.
- New: The thread is in new state if you create an instance of Thread class but before the invocation of start() method.
- Runnable: The thread is in runnable state after invocation of start() method, but the thread scheduler has not selected it to be the running thread.
- Running: The thread is in running state if the thread scheduler has selected it.
- Non-Runnable (Blocked): This is the state when the thread is still alive, but is currently not eligible to run.
- Terminated: A thread is in terminated or dead state when its run() method exits.
How to create thread: There are two ways to create a thread:
- By extending Thread class
- By implementing Runnable interface.
Thread class:
Thread class provide constructors and methods to create and perform operations on a thread.Thread class extends Object class and implements Runnable interface.
Runnable interface:
The Runnable interface should be implemented by any class whose instances are intended to be executed by a thread. Runnable interface have only one method named run().
public void run(): is used to perform action for a thread.
Starting a thread:
start() method of Thread class is used to start a newly created thread. It performs following tasks:
A new thread starts(with new callstack).
The thread moves from New state to the Runnable state.
When the thread gets a chance to execute, its target run() method will run.
1) Java Thread Example by extending Thread class
class Multi extends Thread{
public void run(){
System.out.println("thread is running...");
}
public static void main(String args[]){
Multi t1=new Multi();
t1.start();
}
}
Output:thread is running...
2) Java Thread Example by implementing Runnable interface
class Multi3 implements Runnable{
public void run(){
System.out.println("thread is running...");
}
public static void main(String args[]){
Multi3 m1=new Multi3();
Thread t1 =new Thread(m1);
t1.start();
}
}
Output:thread is running...
Sleep method in java
The sleep() method of Thread class is used to sleep a thread for the specified amount of time.
Syntax of sleep() method in java
The Thread class provides two methods for sleeping a thread:
public static void sleep(long miliseconds)throws InterruptedException
public static void sleep(long miliseconds, int nanos)throws InterruptedException
Example of sleep method in java
class TestSleepMethod1 extends Thread{
public void run(){
for(int i=1;i<5;i++){
try{Thread.sleep(500);}catch(InterruptedException e){System.out.println(e);}
System.out.println(i);
}
}
public static void main(String args[]){
TestSleepMethod1 t1=new TestSleepMethod1();
TestSleepMethod1 t2=new TestSleepMethod1();
t1.start();
t2.start();
}
}
The join() method
The join() method waits for a thread to die. In other words, it causes the currently running threads to stop executing until the thread it joins with completes its task.
Syntax:
public void join()throws InterruptedException
public void join(long milliseconds)throws InterruptedException
Example of join() method
class TestJoinMethod1 extends Thread{
public void run(){
for(int i=1;i<=5;i++){
try{
Thread.sleep(500);
}catch(Exception e){System.out.println(e);}
System.out.println(i);
}
}
public static void main(String args[]){
TestJoinMethod1 t1=new TestJoinMethod1();
TestJoinMethod1 t2=new TestJoinMethod1();
TestJoinMethod1 t3=new TestJoinMethod1();
t1.start();
try{
t1.join();
}catch(Exception e){System.out.println(e);}
t2.start();
t3.start();
}
}
Priority of a Thread (Thread Priority):
Each thread have a priority. Priorities are represented by a number between 1 and 10. In most cases, thread schedular schedules the threads according to their priority (known as preemptive scheduling). But it is not guaranteed because it depends on JVM specification that which scheduling it chooses.
3 constants defiend in Thread class:
public static int MIN_PRIORITY
public static int NORM_PRIORITY
public static int MAX_PRIORITY
Default priority of a thread is 5 (NORM_PRIORITY). The value of MIN_PRIORITY is 1 and the value of MAX_PRIORITY is 10.
Example of priority of a Thread:
class TestMultiPriority1 extends Thread{
public void run(){
System.out.println("running thread name is:"+Thread.currentThread().getName());
System.out.println("running thread priority is:"+Thread.currentThread().getPriority());
}
public static void main(String args[]){
TestMultiPriority1 m1=new TestMultiPriority1();
TestMultiPriority1 m2=new TestMultiPriority1();
m1.setPriority(Thread.MIN_PRIORITY);
m2.setPriority(Thread.MAX_PRIORITY);
m1.start();
m2.start();
}
}
Daemon Thread in Java
Daemon thread in java is a service provider thread that provides services to the user thread. Its life depend on the mercy of user threads i.e. when all the user threads dies, JVM terminates this thread automatically.
There are many java daemon threads running automatically e.g. gc, finalizer etc.
You can see all the detail by typing the jconsole in the command prompt. The jconsole tool provides information about the loaded classes, memory usage, running threads etc.
Points to remember for Daemon Thread in Java
It provides services to user threads for background supporting tasks. It has no role in life than to serve user threads.
- Its life depends on user threads.
- It is a low priority thread.
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