How can I get a first element from a sorted list

Question

I used Collections sort playersList   to sort a List  So  I think playersList is sorted now  But how can I get the first element of the list  playersList 0  does not work

User · Answer

Matthew s answer is correct   list get 0     To do what you tried   list 0     you ll have to wait until Java 7 is released   devoxx conference http   img718 imageshack us img718 11 capturadepantalla201003cg png  Here s an interesting presentation by Mark Reinhold about Java 7   It looks like parleys site is currently down  try later

User · Answer

Using Java 8 streams  you can turn your list into a stream and get the first item in a list using the  findFirst   method   List lt String gt  stringsList   Arrays asList  zordon    alpha    tommy    Optional lt String gt  optional   stringsList stream   findFirst    optional get        zordon    The  findFirst   method will return an Optional that may or may not contain a string value  it may not contain a value if the stringsList is empty    Then to unwrap the item from the Optional use the  get   method

User · Answer

If you just want to get the minimum of a list  instead of sorting it and then getting the first element  O N log N    you can use do it in linear time using min    lt T extends Object  amp  Comparable lt   super T gt  gt  T min Collection lt   extends T gt  coll    That looks gnarly at first  but looking at your previous questions  you have a List lt String gt   In short  min works on it   For the long answer  all that super and extends stuff in the generic type constraints is what Josh Bloch calls the PECS principle  usually presented next to a picture of Arnold -- I M NOT KIDDING       Producer Extends  Consumer Super   It essentially makes generics more powerful  since the constraints are more flexible while still preserving type safety  see  what is the difference between    super    and    extends    in Java Generics

User · Answer

playersList get 0    Java has limited operator polymorphism   So you use the get   method on List objects  not the array index operator

User · Answer

You have to access lists a little differently than arrays in Java   See the javadocs for the List interface for more information   playersList get 0    However if you want to find the smallest element in playersList  you shouldn t sort it and then get the first element   This runs very slowly compared to just searching once through the list to find the smallest element   For example   int smallestIndex   0  for  int i   1  i  lt  playersList size    i          if  playersList get i   lt  playersList get smallestIndex           smallestIndex   i     playersList get smallestIndex     The above code will find the smallest element in O n  instead of O n log n  time

User · Answer

That depends on what type your list is  for ArrayList use   list get 0     for LinkedList use   list getFirst      if you like the array approach   list toArray   0

User · Answer

If your collection is not a List  and thus you can t use get int index    then you can use the iterator   Iterator iter   collection iterator    if  iter hasNext          Object first   iter next

User · Answer

public class Main        public static List lt String gt  list   new ArrayList         public static void main String   args             List lt Integer gt  l   new ArrayList lt  gt              l add 222           l add 100           l add 45           l add 415           l add 311            l sort null           System out println l get 0              without l sort null  returned 222  with l sort null  returned 45

[java] How can I get a first element from a sorted list?

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