I will summarize the methods of List. We plan to update it from time to time.
add(E e) Adds the specified element to the end of this list.
List<String> list = new ArrayList<>();
list.add("Ah");
list.add("Eo");
list.add("asdf");
System.out.println(list);
[Ah,Eo, asdf]
add(int index, E element) Inserts the specified element at the specified position in the list.
List<String> list = new ArrayList<>();
list.add("Ah");
list.add("Eo");
//Insert at 0th
list.add(0, "ABCD");
list.add("asdf");
System.out.println(list);
[ABCD,Ah,Eo, asdf]
clear() Remove all elements from this list.
List<String> list = new ArrayList<>();
list.add("Ah");
list.add("Eo");
list.add(0, "ABCD");
list.add("asdf");
System.out.println(list);
list.clear();
System.out.println(list);
[ABCD,Ah,Eo, asdf]
[]
contains(Object o) Returns true if the specified element is included in this list.
List<String> list = new ArrayList<>();
list.add("Ah");
list.add("Eo");
list.add(0, "ABCD");
list.add("asdf");
//"asdf"Is included in the list, so true
System.out.println(list.contains("asdf"));
//"a"Is not included in the list, so false
System.out.println(list.contains("a"));
true
false
containsAll(Collection<?> c) Returns true if all elements of the specified collection are included in this list.
List<String> list = new ArrayList<>();
List<String> list3 = new ArrayList<>();
List<String> list4 = new ArrayList<>();
list.add("Ai");
list.add("up");
list.add(0, "AB");
list3.add("Ai");
list3.add("up");
list3.add(0, "AB");
list4.add("Ai");
list4.add("U");
list4.add(0, "AB");
//true because the elements contained in list and list3 are the same
System.out.println(list.containsAll(list3));
//false because the elements contained in list and list4 are different
System.out.println(list.containsAll(list4));
true
false
equals(Object o) Compares whether the specified object is equal to this list.
List<String> list = new ArrayList<>();
List<String> list3 = new ArrayList<>();
List<String> list4 = new ArrayList<>();
list.add("Ai");
list.add("up");
list.add(0, "AB");
list3.add("Ai");
list3.add("up");
list3.add(0, "AB");
list4.add("Ai");
list4.add("U");
list4.add(0, "AB");
System.out.println(list.equals(list3));
System.out.println(list.equals(list4));
true
false
get(int index) Returns the element at the specified position in this list.
List<String> list = new ArrayList<>();
list.add("Ai");
list.add("up");
list.add(0, "AB");
System.out.println(list.get(1));
System.out.println(list.get(2));
//IndexOutOfBoundsException
System.out.println(list.get(3));
Ai
up
IndexOutOfBoundsException
hashCode() Returns the hash code value for this list.
List<String> list = new ArrayList<>();
list.add("Ai");
list.add("up");
list.add(0, "AB");
System.out.println(list.hashCode());
14680320
indexOf(Object o) Returns the index of the position where the specified element was first found in this list. Returns -1 if the specified element is not in this list.
List<String> list = new ArrayList<>();
list.add("Ai");
list.add("up");
list.add(0, "AB");
System.out.println(list.indexOf("Ai"));
System.out.println(list.indexOf("AB"));
System.out.println(list.indexOf("ｑ"));
1
0
-1
isEmpty() Returns true if there are no elements in this list.
List<String> list = new ArrayList<>();
List<String> list3 = new ArrayList<>();
List<String> list4 = new ArrayList<>();
list.add("Ai");
list.add("up");
list.add(0, "AB");
list3.add("");
//False because there is an element
System.out.println(list.isEmpty());
//False because the element contains blanks
System.out.println(list3.isEmpty());
//True because there are no elements
System.out.println(list4.isEmpty());
false
false
true
lastIndexOf(Object o) Returns the index of the position where the specified element was last found in this list. Returns -1 if the specified element is not in this list.
List<String> list = new ArrayList<>();
list.add("Ai");
list.add("Ai");
list.add("up");
//The last position to be detected is 1
System.out.println(list.lastIndexOf("Ai"));
//"Ah"Does not exist, so-1
System.out.println(list.lastIndexOf("Ah"));
1
-1
remove(int index) Deletes the element at the specified position in this list.
List<String> list = new ArrayList<>();
list.add("Ai");
list.add("Ai");
list.add("up");
System.out.println(list);
System.out.println(list.remove(1));
System.out.println(list);
[Ai, Ai,up]
Ai
[Ai,up]
remove(Object o) If the specified element is in this list, the first one is removed from the list.
List<String> list = new ArrayList<>();
list.add("Ai");
list.add("Ai");
list.add("up");
System.out.println(list);
//Can be deleted even if characters are specified
list.remove("Ai");
System.out.println(list);
[Ai, Ai,up]
[Ai,up]
removeAll(Collection<?> c) Removes all elements from the specified collection from this list.
List<String> list = new ArrayList<>();
list.add("Ai");
list.add("Ai");
list.add("up");
System.out.println(list);
list.removeAll(list);
System.out.println(list);
[Ai, Ai,up]
[]
retainAll(Collection<?> c) Keeps only the elements contained in the specified collection in this list.
List<String> list = new ArrayList<>(Arrays.asList("Apple","Orange", "Melon"));
List<String> list3 = new ArrayList<>(Arrays.asList("Orange","Melon"));
//Keep only those whose list contains the same elements as list3
list.retainAll(list3);
System.out.println(list);
[Orange, Melon]
set(int index, E element) Replaces the element at the specified position in this list with the specified element.
List<String> list = new ArrayList<>(Arrays.asList("Apple","Orange", "Melon"));
//0th"Apple"When"Banana"To replace
list.set(0, "Banana");
System.out.println(list);
[Banana, Orange, Melon]
size() Returns the number of elements in this list.
List<String> list = new ArrayList<>(Arrays.asList("Apple","Orange", "Melon"));
System.out.println(list.size());
list.add("Banana");
//Since it was added just before, the number of elements increased
System.out.println(list.size());
3
4
subList(int fromIndex, int toIndex) Returns a view of the part of this list from the specified fromIndex (including it) to toIndex (not including it).
ArrayList<Integer> foo = new ArrayList<>(Arrays.asList(10, 30, 5, 1, 11, 90));
System.out.println(foo.subList(0, 3));
System.out.println(foo.subList(1, 2));
System.out.println(foo.subList(4, 5));
[10, 30, 5]
[30]
[11]
toArray(T[] a) Returns an array containing all the elements in this list in the proper order (first element to last element). To convert from a list to an array, use the toArray method.
List<String> list = new ArrayList<>(Arrays.asList("Apple","Orange", "Melon"));
String[] str = new String[list.size()];
list.toArray(str);
System.out.println(Arrays.toString(str));
System.out.println(list);
[Apple, Orange, Melon]
[Apple, Orange, Melon]
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