Java sum elements in arraylist

Sum values in list

This example will show how to sum elements of an arraylist made of numbers using java, java 8 and apache commons. If you are looking for more than just sum, the same reduction technique can be found in average of an ArrayList, finding min of numbers in ArrayList and finding the max value in ArrayList. In a comparable example we demonstrate how to sum numbers in an arraylist using groovy.

Setup

private static ListDouble> NUMBERS_FOR_SUM; @Before public void setup ()  NUMBERS_FOR_SUM = new ArrayListDouble>(); NUMBERS_FOR_SUM.add(new Double(10)); NUMBERS_FOR_SUM.add(new Double(10)); NUMBERS_FOR_SUM.add(new Double(10)); NUMBERS_FOR_SUM.add(new Double(10)); NUMBERS_FOR_SUM.add(new Double(10)); NUMBERS_FOR_SUM.add(new Double(10)); NUMBERS_FOR_SUM.add(new Double(10)); NUMBERS_FOR_SUM.add(new Double(10)); NUMBERS_FOR_SUM.add(new Double(10)); NUMBERS_FOR_SUM.add(new Double(10)); >

Straight up Java

This snippet will sum all digits in an ArrayList using a standard java technique. We will initialize a variable sum and with each iteration of the java 5 for loop add the element to the total which will result to the sum of all numbers in the list.

@Test public void sum_values_in_list_java ()  Double sum = new Double(0); for (Double i : NUMBERS_FOR_SUM)  sum = sum + i; > assertEquals(100, sum, 0); >

Java 8

This snippet will sum all values in an ArrayList using java 8 techniques. Java 8 Streams contains reduce operations which provides an internal implementation of sum that enables a cleaner, more maintainable, and eloquent of way of handling summing all elements in an ArrayList. If you are looking to calculate all reduction operations, DoubleSummaryStatistics example is a class which will calculate all statistics such as average, count, min max and sum.

@Test public void sum_values_in_list_java_8()  double sum = NUMBERS_FOR_SUM.stream().reduce(0d, (a, b) -> a + b); assertEquals(100, sum, 0); // or double sum2 = NUMBERS_FOR_SUM .stream() .mapToDouble(Double::doubleValue) .sum(); assertEquals(100, sum2, 0); >

Apache Commons

This snippet will use apache commons to sum all of the values in an ArrayList using StatUtils which provides static methods for computing statistics.

@Test public void sum_values_in_list_apache()  double[] arrayToSume = ArrayUtils.toPrimitive(NUMBERS_FOR_SUM .toArray(new Double[NUMBERS_FOR_SUM.size()])); double sum = StatUtils.sum(arrayToSume); assertEquals(100, sum, 0); >

Sum values in list posted by Justin Musgrove on 29 January 2014

Tagged: java and java-collections

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5 Ways to Sum Elements in an ArrayList in Java: A Comprehensive Guide

Learn how to sum elements in an ArrayList in Java with our comprehensive guide. Discover 5 methods, including IntStream, stream filter, loop, and Collections.max().

• Converting ArrayList to IntStream to sum elements in Java
• Using stream filter to sum elements of a list in Java
• Looping through the array to sum elements in Java
• Finding the largest element in an array using ArrayList in Java
• Other useful ArrayList methods in Java
• Other helpful code examples for the inbuilt method to sum the elements of an ArrayList in Java
• Conclusion
• How do you sum elements in a list in Java?
• Which method is used to add an element into an ArrayList?
• Does ArrayList have an add method?
• Which method can be used to find the number of elements present inside ArrayList?

If you’re working with Java and have an ArrayList of integers, you might run into a problem of calculating the sum of its elements. Unfortunately, there is no inbuilt method in Java to do this. However, there are several ways to solve this problem. In this article, we will guide you through five different solutions to sum the elements in an ArrayList in Java.

Converting ArrayList to IntStream to sum elements in Java

The first solution is to convert the ArrayList to an IntStream and use its built-in sum() method to calculate the total sum of its elements. Here is an example code snippet:

ArrayListInteger> list = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5)); int sum = list.stream().mapToInt(Integer::intValue).sum(); 

In this code, we first create an ArrayList of integers and then convert it to an IntStream using the stream() method. After that, we map each element to an integer using the mapToInt() method and then call the sum() method to get the total sum.

This solution is concise and efficient. However, it has a limitation. It can only be used with ArrayLists that contain integers. If the ArrayList contains other types of data, we cannot use this solution.

Using stream filter to sum elements of a list in Java

Another solution is to use the stream filter method to sum the elements of an ArrayList in Java. Here is a code example:

ArrayListInteger> list = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5)); int sum = list.stream().filter(i -> i != null).mapToInt(Integer::intValue).sum(); 

In this code, we use the filter method to exclude null values from the ArrayList. After that, we use the mapToInt() method to convert each element to an integer and then call the sum() method to get the total sum.

This solution is flexible and can be used with ArrayLists that contain any type of data. However, it has a limitation. It cannot handle null values in the ArrayList.

Looping through the array to sum elements in Java

The third solution is to use a loop to iterate through the ArrayList and sum the elements. Here is an example code snippet:

ArrayListInteger> list = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5)); int sum = 0; for (Integer i : list)  sum += i; > 

In this code, we first declare a sum variable and initialize it to zero. After that, we use a for-each loop to iterate through each element of the ArrayList and add it to the sum variable.

This solution is simple and can be used with any type of ArrayList. However, it has a limitation. It is not efficient for large ArrayLists as it requires iterating through each element.

Finding the largest element in an array using ArrayList in Java

The fourth solution is to find the largest element in the ArrayList using the Collections.max() method and then subtract it from the sum of all elements. Here is an example code snippet:

ArrayListInteger> list = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5)); int max = Collections.max(list); int sum = list.stream().mapToInt(Integer::intValue).sum() - max; 

In this code, we first find the largest element in the ArrayList using the Collections.max() method. After that, we calculate the sum of all elements using the same method we used in the first solution. Finally, we subtract the maximum element from the sum to get the total sum.

This solution is efficient and can be used with ArrayLists that contain any type of data. However, it has a limitation. It assumes that the ArrayList is not empty. If the ArrayList is empty, it will throw an exception.

Other useful ArrayList methods in Java

Apart from the solutions we have discussed so far, there are several other useful arraylist methods in java that can be used for various purposes. Here are some examples:

• size(): This method returns the number of elements in the ArrayList.
• add(): This method adds an element to the end of the ArrayList.
• retainAll(): This method removes all elements from the ArrayList except those in the specified collection.
• set(): This method replaces the element at the specified position in the ArrayList with the specified element.
• indexOf(): This method returns the index of the first occurrence of the specified element in the ArrayList.

Other helpful code examples for the inbuilt method to sum the elements of an ArrayList in Java

In java, sum of arraylist java 8 code example

int total = numbers.stream().mapToInt(i -> i.intValue()).sum(); System.out.print(total);

In typescript, inbuild method to sum of an arraylist elements in java code example

doubleList.stream().reduce((a,b)->a+b).get(); 

In java, inbuild method to sum of an arraylist elements in java code example

//If you have a List int sum = list.stream().mapToInt(Integer::intValue).sum();//If it's an int[] int sum = IntStream.of(a).sum();

Conclusion

In this article, we have discussed five different solutions to sum the elements in an ArrayList in Java. Each solution has its own advantages and limitations. Therefore, we recommend that you choose the solution that best suits your needs. We have also discussed some useful ArrayList methods in Java that can be used for various purposes. We hope this comprehensive guide has been helpful to you in solving your problem. Remember to always understand the available methods for working with arraylists in java and apply best practices for working with them.

Источник

How to sum the elements of a List in Java

Java FAQ: How do I get the sum of a List in Java (i.e., an ArrayList or LinkedList of numeric values)?

Note: In this article I describe how to sum the elements of a List in Java. This is an interesting exercise, but in general you should use the Apache Commons libraries to calculate the sum (including ListUtils, StatUtils, MathUtils, and more). There are also new techniques in Java 8 (including Stream reduction) that I don’t know very well yet.

Source code to sum the elements of a List

There may be better ways to calculate the sum of the elements in a List in Java than this, but the following example shows the source code for a Java “sum the integers in a list” method:

public static int sum(List list) < int sum = 0; for (int i: list) < sum += i; >return sum; >

I define a sum method like that in a MathUtils class, and call it like this to sum the contents of a List :

// create a list List ints = Arrays.asList(1, 2, 3); // get the sum of the elements in the list int sum = MathUtils.sum(ints);

I shared this sum method in a short post yesterday about how to create and populate a static List in Java, and thought I’d write a bit more about it today. As you can see, this method is written to get the sum of a list of integers, but you can use the same technique to sum double and float values as well.

Note that one thing you have to be careful with in an algorithm like this is that if you’re working with very large numbers, the sum of a list of integers may end up being a long value. (Most “sum” algorithms don’t account for this, but I thought I should mention it.)

In summary, if you needed to see how to sum the elements in a Java List , I hope that is helpful.

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