How to get maximum value from the Collection for example ArrayList

Question

There is an ArrayList which stores integer values  I need to find the maximum value in this list  E g  suppose the arrayList stored values are   10  20  30  40  50 and the max  value would be 50   What is the efficient way to find the maximum value    Edit   I just found one solution for which I am not very sure   ArrayList lt Integer gt  arrayList   new ArrayList lt Integer gt     arrayList add 100      add 200   add 250  add 350  add 150  add 450     Integer i   Collections max arrayList    and this returns the highest value   Another way to compare the each value e g  selection sort or binary sort algorithm  nbsp

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Java 8

As integers are comparable we can use the following one liner in:

List<Integer> ints = Stream.of(22,44,11,66,33,55).collect(Collectors.toList());
Integer max = ints.stream().mapToInt(i->i).max().orElseThrow(NoSuchElementException::new); //66
Integer min = ints.stream().mapToInt(i->i).min().orElseThrow(NoSuchElementException::new); //11

Another point to note is we cannot use Funtion.identity() in place of i->i as mapToInt expects ToIntFunction which is a completely different interface and is not related to Function. Moreover this interface has only one method applyAsInt and no identity() method.

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Comparator comparing  In Java 8  Collections have been enhanced by using lambda  So finding max and min can be accomplished as follows  using Comparator comparing   Code    List lt Integer gt  ints   Stream of 12  72  54  83  51  collect Collectors toList     System out println  the list      ints forEach  i  - gt        System out print i             System out println      Integer minNumber   ints stream            min Comparator comparing i - gt  i   get    Integer maxNumber   ints stream            max Comparator comparing i - gt  i   get     System out println  Min number is     minNumber   System out println  Max number is     maxNumber     Output     the list  12 72 54 83 51    Min number is 12   Max number is 83

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In addition to gotomanners answer  in case anyone else came here looking for a null safe solution to the same problem  this is what I ended up with  Collections max arrayList  Comparator nullsFirst Comparator naturalOrder

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There is no particularly efficient way to find the maximum value in an unsorted list -- you just need to check them all and return the highest value

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Here are three more ways to find the maximum value in a list  using streams   List lt Integer gt  nums   Arrays asList -1  2  1  7  3   Optional lt Integer gt  max1   nums stream   reduce Integer  max   Optional lt Integer gt  max2   nums stream   max Comparator naturalOrder     OptionalInt max3   nums stream   mapToInt p- gt p  max    System out println  max1      max1 get        max2          max2 get        max3      max3 getAsInt       All of these methods  just like Collections max  iterate over the entire collection  hence they require time proportional to the size of the collection

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We can simply use Collections max   and Collections min   method   public class MaxList       public static void main String   args            List l   new ArrayList            l add 1           l add 2           l add 3           l add 4           l add 5           System out println Collections max l       5         System out println Collections min l       1

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model  list stream   max Comparator comparing Model  yourSortList   get

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depending on the size of your array a multithreaded solution might also speed up things

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Here is the fucntion  public int getIndexOfMax ArrayList lt Integer gt  arr       int MaxVal   arr get 0      take first as MaxVal     int indexOfMax   -1    returns -1 if all elements are equal     for  int i   0  i  lt  arr size    i                if current is less then MaxVal         if arr get i   lt  MaxVal                MaxVal   arr get i      put it in MaxVal             indexOfMax   i     put index of current Max                     return indexOfMax

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You can use the Collections API to achieve what you want easily - read efficiently - enough Javadoc for Collections max  Collections max arrayList        Returns the maximum element of the given collection  according to the natural ordering of its elements  All elements in the collection must implement the Comparable interface

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This question is almost a year old but I have found that if you make a custom comparator for objects you can use Collections max for an array list of objects    import java util Comparator   public class compPopulation implements Comparator lt Country gt        public int compare Country a  Country b            if  a getPopulation    gt  b getPopulation                return -1     highest value first         if  a getPopulation      b Population                return 0          return 1          ArrayList lt Country gt  X   new ArrayList lt Country gt        create some country objects and put in the list Country ZZ   Collections max X  new compPopulation

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public int getMax ArrayList list       int max   Integer MIN VALUE      for int i 0  i lt list size    i             if list get i   gt  max               max   list get i                       return max      From my understanding  this is basically what Collections max   does  though they use a comparator since lists are generic

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In Java8  arrayList stream             reduce Integer  max            get

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Integer class implements Comparable So we can easily get the max or min value of the Integer list   public int maxOfNumList         List lt Integer gt  numList   new ArrayList lt  gt         numList add 1       numList add 10       return Collections max numList       If a class does not implements Comparable and we have to find max and min value then we have to write our own Comparator   List lt MyObject gt  objList   new ArrayList lt MyObject gt     objList add object1   objList add object2   objList add object3   MyObject maxObject   Collections max objList  new Comparator lt MyObject gt           Override     public int compare MyObject o1  MyObject o2            if  o1 getValue      o2 getValue                  return 0            else if  o1 getValue    gt  o2 getValue                  return -1            else if  o1 getValue    lt  o2 getValue                  return 1                    return 0

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package in co largestinarraylist   import java util ArrayList  import java util Scanner   public class LargestInArrayList        public static void main String   args             int n          ArrayList lt Integer gt  L   new ArrayList lt Integer gt             int max          Scanner in   new Scanner System in           System out println  Enter Size of Array List            n   in nextInt            System out println  Enter elements in Array List             for  int i   0  i  lt  n  i                  L add in nextInt                        max   L get 0            for  int i   0  i  lt  L size    i                  if  L get i   gt  max                    max   L get i                                    System out println  Max Element      max           in close

[java] How to get maximum value from the Collection (for example ArrayList)?

Java 8

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