Timer java code does not work

[mariapatrawala]

public interface IncDec
{
void increment();
void decrement();
}
public class MyIncDec implements IncDec
{
private int x;
public MyIncDec(int x) {
this.x = x;
}
public void increment() {
this.x++;
}
public void decrement() {
this.x--;
}
}
Part 1: Implement a class which can be used to measure how long each invocation of the increment and decrement method takes (in
milliseconds) and prints out this information. The class should fit in more or less transparently with existing clients of the IncDec interface.

My Solution:

public class Test{
public static void main(String[] args){
MyIncDec mid = new MyIncDec(4);
long l1;
long l2;

l1 = Calendar.getInstance().getTimeInMillis();
mid.increment();
l2 = Calendar.getInstance().getTimeInMillis();
System.out.println(l2-l1);
}
}

My Solution gives me the time diff as 0. When I display the long values before n after calling 'increment', They are the same. Why so?

Thanks,

[eRaaaa]

maybe the execution time is < 1 ms ?

		l1 = System.nanoTime();
		mid.increment();
		l2 = System.nanoTime();
		System.out.println((l2-l1)/(1000*1000d)+" ms");

???

[makpandian]

Better use System.currentTimeMillis() in your program.

[mariapatrawala]

@eRaaaa
Thanks, it did work.

[mariapatrawala]

@makpandian
Yet the time diff is 0.

[makpandian]

that does mean that your exe time is less than milli seconds

[mariapatrawala]

Yes....maybe. Suppose if I had to something similar (timing of method calls) for many places in an application. One idea would be to write a separate timer class for all different methods. Does anyone have another optimized idea to get timing more conveniently?

[mariapatrawala]

In what ways can the following code be improved?

public static final Integer multiply(Integer x, Integer y) {
return (y == 0) ? 0 : multiply(x, y - 1) + x;
}

[JosAH]

In what ways can the following code be improved?

public static final Integer multiply(Integer x, Integer y) {
return (y == 0) ? 0 : multiply(x, y - 1) + x;
}

Improved in what respect? For one thing: your method doesn't work for values of y < 0 but that's easy to fix.

kind regards,

Jos

[mariapatrawala]

Yes and it also won't work for doubles n longs

[JosAH]

Yes and it also won't work for doubles n longs

Of course not because that method takes Integers as parameter types; why not just ints? (primitive); it saves a bunch of (un)boxing operations.

kind regards,

Jos