How to Use Aggregate Functions on a List in Java?

How can I efficiently apply aggregate functions such as sum, average, max, and min on a list in Java?

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);  
int sum = numbers.stream().mapToInt(Integer::intValue).sum();  
double average = numbers.stream().mapToInt(Integer::intValue).average().orElse(0);  
int max = numbers.stream().mapToInt(Integer::intValue).max().orElse(Integer.MIN_VALUE);  
int min = numbers.stream().mapToInt(Integer::intValue).min().orElse(Integer.MAX_VALUE);

In Java, you can utilize the Stream API introduced in Java 8 to perform aggregate operations on lists. These operations include calculating the sum, average, maximum, and minimum values using concise and readable lambda expressions.

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);  
int sum = numbers.stream().mapToInt(Integer::intValue).sum();  
double average = numbers.stream().mapToInt(Integer::intValue).average().orElse(0);  
int max = numbers.stream().mapToInt(Integer::intValue).max().orElse(Integer.MIN_VALUE);  
int min = numbers.stream().mapToInt(Integer::intValue).min().orElse(Integer.MAX_VALUE);

Causes

• Not understanding the Stream API basics.
• Misusing map and reduce operations.
• Forgetting to include necessary imports.

Solutions

• Use the appropriate Stream methods such as mapToInt(), sum(), average(), max(), min().
• Ensure to check for empty lists to avoid exceptions like NoSuchElementException.
• Understand the differences between OptionalInt and int to avoid confusion.

Mistake: Not checking if the list is empty before calling aggregate methods.

Solution: Use Optional methods like orElse() to provide default values.

Mistake: Using IntStream inappropriately without converting types.

Solution: Always use mapToInt for Integer lists to perform aggregate functions.