How to Use Java 8 Lambda with Collectors.summingLong for Multiple Columns?

How can I efficiently use Java 8's Collectors.summingLong to sum values from multiple columns in a stream?

List<YourObject> list = ...; // Assumes YourObject has methods getColumn1() and getColumn2()
long sum = list.stream()
               .collect(Collectors.summingLong(obj -> obj.getColumn1() + obj.getColumn2()));

In Java 8, you can utilize the Stream API along with Collectors.summingLong to perform operations such as summing values from multiple fields. The Collectors.summingLong method sums long values extracted from stream elements, allowing for concise and readable code for summing multiple columns from your data classes.

// Example of summing multiple columns from a list of objects
import java.util.List;
import java.util.stream.Collectors;

class YourObject {
    private long column1;
    private long column2;

    public long getColumn1() { return column1; }
    public long getColumn2() { return column2; }
}

List<YourObject> list = ...;
long totalSum = list.stream()
                   .collect(Collectors.summingLong(obj -> obj.getColumn1() + obj.getColumn2()));
System.out.println("Total Sum: " + totalSum);

Causes

• In scenarios where you need to aggregate data from collections of objects.
• When working with streams and needing to perform operations on multiple fields.

Solutions

• Use Collectors.summingLong with a lambda expression to sum values from different columns in an object.
• Combine values from multiple columns within the lambda expression before passing it to Collectors.summingLong.

Mistake: Forgetting to cast the result of the sum to a long when using non-long types.

Solution: Ensure you're summing long values or casting appropriately. Use getColumn().longValue() if you're dealing with Long objects.

Mistake: Not handling null values in your object properties which could lead to NullPointerExceptions.

Solution: Consider using Optional to safely handle potential null values. For instance: Collectors.summingLong(obj -> Optional.ofNullable(obj.getColumn1()).orElse(0L) + Optional.ofNullable(obj.getColumn2()).orElse(0L))