如何在Java中为特定类型迭代对象的ArrayList

Question

I am trying to iterate through an ArrayList myWaste, of waste objects.

Some of these waste objects are of type "packaging", from the Packaging class, and the objects of type "packaging" need to be counted, and the count needs to be returned.

I have tried with a for each loop but I am not having much luck:

int count = 0;
for (Waste packaging : myWaste){
    count += 1;
}
return count;

Answer 1

Try this:

int count = 0;
for(myWaste mw : myWaste)
   if(mw instanceof Packaging)
      count++;

Or if you wanna try lambdas with java8+ :

int count = myWaste.stream().filter(myWaste -> myWaste instanceof Packaging).count();

Answer 2

If I'm not mistake, try this:

int count = 0;
for (Waste packaging : myWaste){
    if (packaging instanceof Packaging) {
        count += 1;
    }
}
return count;