Use of Private Constructor in Thread Example

[Sandra Bachan]

Head First Java, Page 526, typed this up verbatim:

public class TestThreads{
	public static void main(String[] args){
		ThreadOne t1 = new ThreadOne();
		ThreadTwo t2 = new ThreadTwo();
		Thread one = new Thread(t1);
		Thread two = new Thread(t2);
		one.start();
		two.start();
	}
}

class Accum{
	private static Accum a = new Accum();
	private int counter = 0;

	private Accum(){}

	private static Accum getAccum(){
		return a;
	}

	public void updateCounter(int add){
		counter += add;
	}

	public int getCount(){
		return counter;
	}
}

class ThreadOne implements Runnable{
	Accum a = Accum.getAccum();
	
	public void run(){
		for (int x=0; x<98; x++){
			a.updateCounter(1000);
			try{
				Thread.sleep(50);
			}catch(InterruptedException ex){}
		}
		System.out.println("one " + a.getCount());
	}
}

class ThreadTwo implements Runnable{
	Accum a = Accum.getAccum();

	public void run(){
	
		for(int x=0; x<99; x++){
			a.updateCounter(1);
			try{
				Thread.sleep(50);
			}catch(InterruptedException ex){}
		}
		System.out.println("two " +a.getCount());
	
	}
}

Why is the compiler outputting:



TestThreads.java:32: getAccum() has private access in Accum
Accum a = Accum.getAccum();
^
TestThreads.java:46: getAccum() has private access in Accum
Accum a = Accum.getAccum();
^
2 errors


Please explain

[Suresh Babu Venkat]

Thats because the method is private and we cannot access methods which are private from anywhere other than with in the same class

[Abimaran Kugathasan]

Sandra Bachan wrote:
Why is the compiler outputting:
TestThreads.java:32: getAccum() has private access in Accum
Accum a = Accum.getAccum();
^
TestThreads.java:46: getAccum() has private access in Accum
Accum a = Accum.getAccum();
^
2 errors
Please explain

Since the method getAccum() in the Accum class has the private access, you can't access it beyond that class. That's why you get Compilation Error! change it to public, then it will Compile perfectly!

public class TestThreads{
	public static void main(String[] args){
		ThreadOne t1 = new ThreadOne();
		ThreadTwo t2 = new ThreadTwo();
		Thread one = new Thread(t1);
		Thread two = new Thread(t2);
		one.start();
		two.start();
	}
}

class Accum{
	private static Accum a = new Accum();
	private int counter = 0;

	private Accum(){}

	public static Accum getAccum(){ // Changed the access modifier to public
		return a;
	}

	public void updateCounter(int add){
		counter += add;
	}

	public int getCount(){
		return counter;
	}
}

class ThreadOne implements Runnable{
	Accum a = Accum.getAccum();

	public void run(){
		for (int x=0; x<98; x++){
			a.updateCounter(1000);
			try{
				Thread.sleep(50);
			}catch(InterruptedException ex){}
		}
		System.out.println("one " + a.getCount());
	}
}

class ThreadTwo implements Runnable{
	Accum a = Accum.getAccum();

	public void run(){

		for(int x=0; x<99; x++){
			a.updateCounter(1);
			try{
				Thread.sleep(50);
			}catch(InterruptedException ex){}
		}
		System.out.println("two " +a.getCount());

	}
}