- #1
- 4
- 0
1.Homework Statement +
Hello,
I really need your help, because I'm a Java newbie and I've got stuck in this Java homework.
I should implement class ObjectCounter, which has to include two methods:
Implemented class ObjectCounter has to use the HashMap and all of it has to be called this way:
But it always ends with java.lang.NullPointerException, but I don't know how to repair it.
Thank you very much!
Homework Equations
Hello,
I really need your help, because I'm a Java newbie and I've got stuck in this Java homework.
I should implement class ObjectCounter, which has to include two methods:
Code:
// increase the counter for given object
public void add(Object o)
// returns the current number of objects, i.e. current value of counter
public int getCount(Object o)
Code:
ObjectCounter objectCounter = new ObjectCounter();
objectCounter.add("hi");
// has to print 1
System.out.println(objectCounter.getCount("hi"));
// has to print 0
System.out.println(objectCounter.getCount("hello"));
objectCounter.add("hi");
// has to print 2
System.out.println(objectCounter.getCount("hi"));
objectCounter.add("hello");
// has to print 1
System.out.println(objectCounter.getCount("hello"));
The Attempt at a Solution
Code:
public class ObjectCounter {
private HashMap<Integer, Integer> map = new HashMap();
public void add(Object o) {
int counter = getCount(o);
if (counter == 0) {
map.put(o.hashCode(), 1);
} else {
map.remove(o.hashCode());
map.put(o.hashCode(), counter++);
}
}
public int getCount(Object o) {
System.out.println(map.get(o.hashCode()));
return map.get(o.hashCode());
}
}
Thank you very much!