Please enable JavaScript.

Coggle requires JavaScript to display documents.

Creating collections - Coggle Diagram

- - - - Java 10 added
        
        Collectors.toUnmodifiableList()
  - - - especially Map version
        
        toMap needs
        
        a valueMapper
        
        a keyMapper
        
        Map<String, Integer> result = givenList.stream() .collect(toMap(Function.identity(), String::length))
- - - - 11 with 0 to 10 parameters
      - one with var-args
      - why bother?
        
        every var-args method call implicitly creates an array
        
        the overloaded methods
        
        avoid unnecessary object creation
        
        and garbage collection overhead
    - - results in an IllegalArgumentException at runtime
  - - - with 0 to 10 key-value pairs
      - and a different method for more than 10
        
        Map<String, String> map = Map.ofEntries( new AbstractMap.SimpleEntry<>("foo", "a"), new AbstractMap.SimpleEntry<>("bar", "b"), new AbstractMap.SimpleEntry<>("baz", "c"));
    - - results in an IllegalArgumentException at runtime
  - - - introduced in Java 9
      - internal
      - constructors have restricted access
      - the returned instances are
        
        immutable
        
        can't contain
        
        null elements
        
        in List and Set
        
        null keys
        
        in Map
        
        NullPointerException
- - - - not obvious to look here
        
        for methods to create a List
  - - - but isn't an ArrayList or a LinkedList
      - it's a List
        
        backed by the original array
    - - it has a fixed size
        
        @Test(expected = UnsupportedOperationException.class) public void givenArraysAsList_whenAdd_thenUnsupportedException() { List<String> list = Arrays.asList("foo", "bar"); list.add("baz"); }
      - original array and the list created share the same reference
        
        @Test public void givenArraysAsList_whenCreated_thenShareReference(){ String[] array = {"foo", "bar"}; List<String> list = Arrays.asList(array); array[0] = "baz"; assertEquals("baz", list.get(0)); }
- - - - @Test public void givenAnonymousInnerClass_thenInitialiseList() { List<String> cities = new ArrayList() { { add("New York"); add("Rio"); add("Tokyo"); } }; assertTrue(cities.contains("New York")); }
      - first set of braces
        
        creates an anonymous inner class
        
        subclass of ArrayList
      - second set
        
        creates an instance initialisation block
  - - - java 7 feature
    - - may cause memory leaks