### Example 1: Using Stream.collect()

import java.util.Arrays;

import java.util.List;

import java.util.stream.Collectors;

public class DriverClass {

public static void main(String[] args) {

List<Integer> integers = Arrays.asList(2, 9, 10, 8, 4, 7);

Integer sum = integers.stream()

.collect(Collectors.summingInt(Integer::intValue));

System.out.println("Sum= " + sum);

}

}

Similarly, the Collectors class provides

**summingDouble()**and**summingLong()**### Example 2: Using Stream.reduce()

import java.util.Arrays;

import java.util.List;

import java.util.stream.Collectors;

public class DriverClass {

public static void main(String[] args) {

List<Integer> integers = Arrays.asList(2, 9, 10, 8, 4, 7);

Integer sum = integers.stream()

.reduce(0, (a, b) -> a + b);

System.out.println("Sum="+sum);

}

}

### Example 3: Using IntStream.sum()

import java.util.Arrays;

import java.util.List;

import java.util.stream.Collectors;

public class DriverClass {

public static void main(String[] args) {

List<Integer> integers = Arrays.asList(2, 9, 10, 8, 4, 7);

Integer sum = integers.stream()

.mapToInt(Integer::intValue)

.sum();

System.out.println("Sum= " + sum);

}

}

### Example 4: Sum of all numbers in an array

import java.util.Arrays;

import java.util.List;

import java.util.stream.Collectors;

public class DriverClass {

public static void main(String[] args) {

int[]integers = {2, 9, 10, 8, 4, 7};

int sum = Arrays.stream(integers).sum();

System.out.println("Sum= " + sum);

}

}

### Example 5: Sum of all numbers in a Set

import java.util.Set;

import java.util.stream.Collectors;

import java.util.stream.Stream;

public class DriverClass {

public static void main(String[] args) {

Set<Integer> integers = Stream.of(2, 9, 10, 8, 4, 7).

collect(Collectors.toSet());

Integer sum = integers.stream()

.mapToInt(Integer::intValue)

.sum();

System.out.println("Sum= " + sum);

}

}

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