Is there possibility of sum of ArrayList without looping

Question

Is there possibility of sum of ArrayList without looping   PHP provides sum array  which will give the sum of array   The PHP code is like   a   array 2  4  6  8   echo  sum a        array sum  a      n     I wanted to do the same in Java   List tt   new ArrayList    tt add 1   tt add 2   tt add 3

User · Answer

This link shows three different ways how to sum in java, there is one option that is not in previous answers using Apache Commons Math..

Example:

public static void main(String args []){
    List<Double> NUMBERS_FOR_SUM = new ArrayList<Double>(){
         {
            add(5D);
            add(3.2D);
            add(7D);
         }
    };
    double[] arrayToSume = ArrayUtils.toPrimitive(NUMBERS_FOR_SUM
            .toArray(new Double[NUMBERS_FOR_SUM.size()]));    
    System.out.println(StatUtils.sum(arrayToSume));

}

See StatUtils api

User · Answer

Once java-8 is out  March 2014  you ll be able to use streams   If you have a List lt Integer gt   int sum   list stream   mapToInt Integer  intValue  sum      If it s an int    int sum   IntStream of a  sum

User · Answer

You can use apache commons-collections API   class AggregateClosure implements org apache commons collections Closure           int total   0            Override         public void execute Object input                if  input    null                    total     Integer  input                                   public int getTotal                 return total                    Then use this closure as shown below   public int aggregate List lt Integer gt  aList            AggregateClosure closure   new AggregateClosure            org apache commons collections CollectionUtils forAllDo aList  closure           return closure getTotal

User · Answer

Write a util function like  public class ListUtil       public static int sum List lt Integer gt  list         if list  null    list size   lt 1          return 0         int sum   0        for Integer i  list          sum   sum i         return sum            Then use like   int sum   ListUtil sum yourArrayList

User · Answer

Then write it yourself   public int sum List lt Integer gt  list         int sum   0         for  int i   list           sum   sum   i        return sum

User · Answer

ArrayList is a Collection of elements  in the form of list   primitive are stored as wrapper class object but at the same time i can store objects of String class as well  SUM will not make sense in that  BTW why are so afraid to use for loop  enhanced or through iterator  anyways

User · Answer

Given that a list can hold any type of object  there is no built in method which allows you to sum all the elements  You could do something like this   int sum   0   for  Integer i     ArrayList lt Integer gt   tt       sum    i      Alternatively you could create your own container type which inherits from ArrayList but also implements a method called sum   which implements the code above

User · Answer

Or switch to Groovy  it has a sum   function on a collection   1 2 3 4 5 6  sum    http   groovy codehaus org JN1015-Collections   Runs on the same JVM as your java classes

User · Answer

for me the clearest way is this   doubleList stream   reduce  a b - gt a b  get      or   doubleList parallelStream   reduce  a b - gt a b  get      It also use internal loops  but it is not possible without loops

User · Answer

The only alternative to using a loop is to use recursion   You can define a method like  public static int sum List lt Integer gt  ints       return ints isEmpty     0   ints get 0    ints subList 1  ints length         This is very inefficient compared to using a plain loop and can blow up if you have many elements in the list   An alternative which avoid a stack overflow is to use   public static int sum List lt Integer gt  ints        int len   ints size        if  len    0  return 0      if  len    1  return ints get 0       return sum ints subList 0  len 2     sum ints subList len 2  len        This is just as inefficient  but will avoid a stack overflow     The shortest way to write the same thing is  int sum   0  a      2  4  6  8    for int i  a        sum    i     System out println  sum a        sum     prints  sum a    20

User · Answer

You can use GNU Trove library   TIntList tt   new TIntArrayList    tt add 1   tt add 2   tt add 3   int sum   tt sum

User · Answer

This can be done with reduce using method references reduce Integer  sum     Integer reduceSum   Arrays asList 1  3  4  6  4           stream            reduce Integer  sum           get      Or without Optional   Integer reduceSum   Arrays asList 1  3  4  6  4           stream            reduce 0  Integer  sum

User · Answer

If you know about the map function  then you know that a map is also can be recursive loop or recursive loop  But obviously you have to reach each element for that    so  I could not work out the Java 8  because some syntax mismatch but wanted a very short so this is what I got   int sum   0 for  Integer e   myList  sum    e

[java] Is there possibility of sum of ArrayList without looping

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