Learn to use the if-else conditions logic using Java Stream API to filter the items from a collection based on certain conditions.
1. The ‘if-else‘ Condition as Consumer Implementation
The 'if-else' condition can be applied as a lambda expression in forEach() function in form of a Consumer action.
Consumer is a functional interface whose functional method is ‘void accept(Object)‘. It represents an operation that accepts a single input argument and returns no result.
In the given example, we are checking if a number is even then print a message, else print another message for an odd number.
ArrayList<Integer> numberList
= new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5, 6));
Consumer<Integer> action = i -> {
if (i % 2 == 0) {
System.out.println("Even number :: " + i); //Or any other user action we want to do
} else {
System.out.println("Odd number :: " + i); //Or any other user action we want to do
}
};
numberList.stream()
.forEach(action);- We can perform any kind of operation on the stream items instead of just printing the items to the console, e.g. storing the items to two separate lists or passing the items to other method calls.
- We can write as many if-else statements as required.
- We can also write the pass the Consumer implementation as an inline lambda expression to the
forEach()function.
Arrays.asList(-1, 1, -2, 3, 4, -5, 6, 0).stream()
.forEach(
i -> {
if (i == 0) {
System.out.println("Number is 0");
} else if (i > 0) {
System.out.println("Positive Number");
} else {
System.out.println("Negative Number");
}
}
);
2. The ‘if' Condition with Predicates
If we intend to apply only 'if' logic then we can pass the condition directly do the filter() function as a Predicate.
In the given example, we are checking if a number is an even number then printing a message.
ArrayList<Integer> numberList = new ArrayList<>(Arrays.asList(1,2,3,4,5,6));
Predicate<Integer> isEven = i -> i % 2 == 0;
numberList.stream()
.filter(isEven)
.forEach(System.out::println);Using one of the above given two methods, we can apply any combination of if-else conditions in Java 8 stream elements.
Happy Learning !!
int a; list.forEach(i-> { if(i%2==0) a=i; })how to handle this ? variable in lambda should be final or effectively final
Multiple ways to this:
1. use AtomicInteger instead of int.
AtomicInteger a = new AtomicInteger(0);list.forEach(i-> {
if(i%2==0)
a.set(i);
});
int answer = a.get();
2. Refactor: you are looking for last element divisible by 2.
int a = list.stream().filter(i -> i%2 == 0).reduce((first, second) -> second).orElse(null);Why do you suggested to use AtomicInteger instead of int?
The only application of AtomicReference<T> I know is to “explicitly” implement pass by reference — in other words, exchange multiple values to and pro a java method
C allows this by passing &var (in place of var). C++ too
Java allows a single return value. So use AtomicReference<T>
We can as well put all variables we wanna exchange in a single object, pass the object to the java method — but we might feel lazy and/or unnecessary to create a new class just for this purpose
May I know in which other situations are AtomicReference<T>, AtomicInteger, etc useful?