observable

可觀察的類countObservers()方法 (Observable Class countObservers() method)

• countObservers() method is available in java.util package.

  countObservers()方法在java.util包中可用。

• countObservers() method is used to count the number of observers exists in this Observable.

  countObservers()方法用于計算此Observable中存在的觀察者的數量。

• countObservers() method is a non-static method, it is accessible with the class object only and if we try to access the method with the class name then we will get an error.

  countObservers()方法是一個非靜態方法，只能通過類對象訪問，如果嘗試使用類名訪問該方法，則會收到錯誤消息。

• countObservers() method does not throw an exception at the time of counting the observer.

  在計數觀察者時， countObservers()方法不會引發異常。

Syntax:

句法：

    public int countObservers();

Parameter(s):

參數：

• It does not accept any parameter.

  它不接受任何參數。

Return value:

返回值：

The return type of the method is int, it gets the number of observers in this Observable.

方法的返回類型為int ，它獲取此Observable中的觀察者數量。

Example:

例：

// Java program to demonstrate the example 
// of int countObservers() method of Observable
import java.util.*;
// Implement Observers class 
class Observers_1 implements Observer {
public void update(Observable obj, Object ob) {
System.out.println("Obs1: ");
}
}
class Observers_2 implements Observer {
public void update(Observable obj, Object ob) {
System.out.println("Obs2: ");
}
}
// Implement Observed Class
class Observed extends Observable {
// Function call
void countObs() {
setChanged();
// By using notifyObservers() method is 
// to notify all the observers that are
// implemented
notifyObservers();
}
}
public class CountObservers {
// Implement Main Method
public static void main(String args[]) {
Observed observed = new Observed();
Observers_1 obs1 = new Observers_1();
Observers_2 obs2 = new Observers_2();
observed.addObserver(obs1);
observed.addObserver(obs2);
// By using countObservers() method is
// to return the number of observers 
// in this object
int count_obs = observed.countObservers();
System.out.println("observed.countObservers(): " + count_obs);
observed.countObs();
}
}

Output

輸出量

observed.countObservers(): 2
Obs2: 
Obs1: 

翻譯自: https://www.includehelp.com/java/observable-countobservers-method-with-example.aspx

observable