How can I convert the following for loop to use a Java lambda with streams?
List<Fruit> fruits = createFruitArrayList (); // creates a list of fruits
Fruit largeApple = null; // holds the largest apple so far for
for (Fruit fruit : fruits) {
if (fruit.getType () == “Apple”) {
if (largeApple == null ||
largeApple.size () < fruit.size ()) {
largeApple = fruit;
}
}
}
You can use the comparator to compare the two values
Comparator<Fruit> comp = (fruit1, fruit2) -> Integer.compare( fruit1.size(), fruit2.size());
Fruit largeApple = fruits.stream().max(comp).get();
Also the way you compare strings is wrong
if (fruit.getType () == “Apple”)
What you proberly want
if (fruit.getType().equals("Apple"))
For more Information on that, take a look at this question: How do I compare strings in Java?
Danger, Will Robinson! Don't use == to compare strings! Use equals().
That said, this code is equivalent to your loop:
Fruit largestApple = fruits.stream()
.filter(f -> f.getType().equals("Apple"))
.max(Comparator.comparing(Fruit::size))
.orElse(null);
Note the use of a method reference (rather than a lambda) as the parameter passed to comparing().
This looks like it works:
public void test() {
// creates a list of fruits
List<Fruit> fruits = Arrays.asList(
new Fruit("Apple", 10),
new Fruit("Apple", 14),
new Fruit("Pear", 4));
// Old style.
// holds the largest apple so far
Fruit largeApple = null;
for (Fruit fruit : fruits) {
if (fruit.getType().equals("Apple")) {
if (largeApple == null
|| largeApple.size() < fruit.size()) {
largeApple = fruit;
}
}
}
System.out.println("Old: " + largeApple);
// New Style.
Optional<Fruit> max = fruits.stream()
.filter(f -> f.type.equals("Apple"))
.max(Comparator.comparing(f -> f.size));
System.out.println("Lambda: " + max);
}
BTW: Your sample code is terrible - please post a working sample in real syntactically correct java.
