Data update

Task/Topic-variable/Java/topic-variable.java

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+import java.awt.Point;
+import java.util.ArrayDeque;
+import java.util.List;
+import java.util.Queue;
+
+public final class TopicVariable {
+
+	public static void main(String[] args) {
+		List<Integer> numbers = List.of( 1, 2, 3, 4, 5, 6, 7, 8, 9 );
+		// Example 1:		
+		// We only want to count the number of elements in a list,
+		// so a topic variable can be used for the identify of each element of the list.
+		// An artificial example since we could just use 'total = numbers.size()'.
+	    int total = 0;
+	    for ( Integer _ : numbers ) { // Topic variable
+	        total += 1;
+	    }
+	    System.out.println("The list contains " + total + " numbers");
+		
+	    // Example 2:
+	    // A topic variable is suitable for the unused identifier of the NumberFormatException.
+		String text = "123456:@~";
+		int i = 0;
+		try {
+		    i = Integer.parseInt(text);
+		} catch(NumberFormatException _) { // Topic variable
+		    System.out.println("Variable i is incorrectly defined with value: " + i);
+		}
+		
+		// Example 3:
+		// We only require the first two out of every three items in a queue.
+		// A topic variable can be used for the third unused item.
+		Queue<Integer> queue = new ArrayDeque<Integer>(numbers);
+		while ( queue.size() >= 3 ) {
+			int x = queue.poll();
+		    int y = queue.poll();
+		    int _ = queue.poll(); // Topic variable
+		    System.out.println( new Point(x, y) );
+		}
+	}
+
+}