A field to count the amount instances of a class [duplicate]

Question

I need to create a field to count the number of instances made by a class

public class Circle { private int diameter; private int xPosition; private int yPosition; private String color; private boolean isVisible; private static int count = 0; /** * Create a new circle at default position with default color. */ public Circle() { diameter = 30; xPosition = 20; yPosition = 60; color = "blue"; isVisible = false; count = count++; } public void returnCount(){ System.out.println(count); }

This is what Ive been playing with. I was hoping the count would increment by 1 each time a variable is created. However it just stays at 0.

Thanks for any help, Ciaran.

Community · Accepted Answer · 2017-05-23 12:03:22Z

Use just:

count++;

Why? because:

count = count ++;

is similar to doing something like this:

temp = count ; // temp is 0. count = count +1; // increment count count = temp; // assign temp (which is 0) to count.

Take a look at a similar post-increament question.

Sven · Accepted Answer · 2013-12-08 14:07:06Z

The post increment operator implicitly uses a temp variable. so,

count = count ++;

is not equal to

count++;

in java.

lkamal · Accepted Answer · 2013-12-08 13:54:51Z

This is because of the invalid use of ++ operator.

Your code can be corrected simply by correcting the line as below.

// count = count++; incorrect count++; // correct // count = count + 1; // correct

When you use count++, the count variable is incremented by 1; but the value returned from the operator is the previous value of count variable.

You can learn this by trying the below.

public class Test { public static void main(String[] args) { int count = 0; System.out.println(count++); // line 1 System.out.println(count++); } }

When you run above below is the results.

0 1

That is "line 1" prints only 0 since the return value of count++ is always the previous value.

Collectives™ on Stack Overflow

A field to count the amount instances of a class [duplicate]

3 Answers 3

Comments

Comments

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Linked

Related