What does the colon operator do

Question

Apparently a colon is used in multiple ways in Java  Would anyone mind explaining what it does   For instance here   String cardString       for  PlayingCard c   this list       lt --       cardString    c     n       How would you write this for-each loop a different way so as to not incorporate the

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It s used in for loops to iterate over a list of objects   for  Object o  list           o is an element of list here     Think of it as a for  lt item gt  in  lt list gt  in Python

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The colon actually exists in conjunction with    int minVal    a  lt  b    a   b    is equivalent to   int minval  if a  lt  b   minval   a    else  minval   b      Also in the for each loop   for Node n   List l           literally   for Node n   l head  n next    null  n   n next

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How would you write this for-each loop a different way so as to not incorporate the        Assuming that list is a Collection instance      public String toString        String cardString          for  Iterator lt PlayingCard gt  it   this list iterator    it hasNext                  PlayingCard c   it next          cardString   cardString   c     n              I should add the pedantic point that   is not an operator in this context   An operator performs an operation in an expression  and the stuff inside the         in a for statement is not an expression     according to the JLS

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It is used in the new short hand for loop  final List lt String gt  list   new ArrayList lt String gt     for  final String s   list       System out println s       and the ternary operator  list isEmpty     true   false

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There are several places colon is used in Java code   1  Jump-out label  Tutorial    label  for  int i   0  i  lt  x  i          for  int j   0  j  lt  i  j              if  something i  j   break label     jumps out of the i loop             i e  jumps to here   2  Ternary condition  Tutorial    int a    b  lt  4   7  8     if b  lt  4  set a to 7  else set a to 8   3  For-each loop  Tutorial    String   ss     hi    there   for  String s  ss        print s      output  hi    and  there  on the next iteration     4  Assertion  Guide    int a   factorial b   assert a  gt   0   factorial may not be less than 0      throws an AssertionError with the message if the condition evaluates to false   5  Case in switch statement  Tutorial    switch  type        case WHITESPACE      case RETURN          break      case NUMBER          print  got number      value           break      default          print  syntax error        6  Method references  Tutorial   class Person      public static int compareByAge Person a  Person b           return a birthday compareTo b birthday            Arrays sort persons  Person  compareByAge

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Since most for loops are very similar  Java provides a shortcut to reduce the     amount of code required to write the loop called the for each loop   Here is an example of the concise for each loop     for  Integer grade   quizGrades         System out println grade            In the example above  the colon     can be read as  in   The for each loop     altogether can be read as  for each Integer element  called grade  in     quizGrades  print out the value of grade

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There is no  colon  operator  but the colon appears in two places   1  In the ternary operator  e g    int x   bigInt   10000   50    In this case  the ternary operator acts as an  if  for expressions  If bigInt is true  then x will get 10000 assigned to it  If not  50  The colon here means  else    2  In a for-each loop   double   vals   new double 100     fill x with values for  double x   vals          do something with x     This sets x to each of the values in  vals  in turn  So if vals contains  10  20 3  30        then x will be 10 on the first iteration  20 3 on the second  etc   Note  I say it s not an operator because it s just syntax  It can t appear in any given expression by itself  and it s just chance that both the for-each and the ternary operator use a colon

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It will prints the string something  three times   JLabel   labels    new JLabel    new JLabel    new JLabel                         for   JLabel label   labels                                         label setText  something        panel add label

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You usually see it in the ternary assignment operator   Syntax   variable     condition   result 1   result 2     example   boolean isNegative   number  gt  0   false   true    which is  equivalent  in nature to the if else  if number  gt  0       isNegative   false    else      isNegative   true      Other than examples given by different posters   you can also use   to signify a label for a block which you can use in conjunction with continue and break     for example   public void someFunction           an infinite loop      goBackHere      label           for int i   0  i  lt  10  i                    if i    9   continue goBackHere

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In your specific case    String cardString       for  PlayingCard c   this list       lt --       cardString   cardString   c     n       this list is a collection  list  set  or array   and that code assigns c to each element of the collection   So  if this list were a collection   2S    3H    4S   then the cardString on the end would be this string   2S 3H 4S

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Just to add  when used in a for-each loop  the     can basically be read as  in    So  for  String name   names           remainder omitted     should be read  For each name IN names do

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colon is using in for-each loop  Try this example   import java util     class ForEachLoop          public static void main String args             enter code here         Integer   iray  1 2 3 4 5          String   sray   ENRIQUE IGLESIAS           printME iray          printME sray                    public static void printME Integer   i                                        for Integer x i                                          System out println x                                       public static void printME String   i                              for String x i                                          System out println x

[java] What does the colon (:) operator do?

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