how to make an array of arraylists in java
ArrayList<Integer> [] myList = (ArrayList<Integer>[]) new ArrayList[4];how to make an array of arraylists in java
ArrayList<Integer> [] myList = (ArrayList<Integer>[]) new ArrayList[4];list of arrays java
List<int[]> A = new List<int[]>();arrays lists java
ArrayList: part of Collections
does not support primitives, only support none primitives
size is dynamic, automatically adjusted
has index numbers
ArrayList <DataType> listName = new ArrayList <DataType> ();
methods:
add(): adds Objects to the arraylist
get(index): gets the object at the given index, returns the object as it is
size(): returns the length (size) of the arraylist as an int
add(Object): adds objects to the arraylist
add(index, Object): adds the object at the given index
set(index, Object): replacing the original object at given index with the new given object
remove(int index): object at the given index will be removed. ONLY one
remove(Object): given object will be removed, returns boolean. ONLY one
clear(): remove everything from arraylist, size will be 0
indexOf(Object): returns the index number of the object, int
contains(Object): returns boolean
equals(ArrayListName): compares two arrayList
isEmpty(): returns boolean, depeding on the size
Data Structures:
1. Array ==> Arrays (java.util)
2. Collection ==> Collections (java.util), does not support primitive
3. Maps ==> does not support primitive
Methods:
Bulk Operations:
containsAll(CollectionType): verifies if all objects in CollectionType are contained in the list or not, returns boolean
addAll(CollectionType): adds multiple objects, adds all the objects from given collection type
removeAll(CollectionType): removes multiple objetcs, removes all the matching objects
retainAll(CollectionType): removes all the unmatching objects
{1,2,3,4,5,6,7,1,2,3,4}
removeAll(1,2,3,4) ==> {5,6,7}
retainAll(1,2,3,4) ==> {1,2,3,4,1,2,3,4 }
Arrays.asList(object1, object2 ..): returns the collection type (List)
ArrayList<Integer> numList = new ArrayList<>(CollectionType);
sorting arrayList:
Collections.sort(ArrayListName); ==> Ascending order
Collections: presented in "java.util" package
import PakageName.Classname;
import java.util.Collections;
Collections Class:
sort(CollectionType): sorting any given collectionType
frequency(CollectionType, Object): returns the frequency of the given object from the given collectionType
max(CollectionType): return the max object from collectiontype
min(CollectionType): return the min object from collectiontype
swap(CollectionType, index1, index2): swaps the elemnts at the given indexs from the CollectionType
list: {1,2,3,4,5}
Collections.swap(list, 1, 2); ==> {1,3,2,4,5}
replaceAll(CollectionType, oldValue, newValue):
list: {1,1,1,2,3,4,5}
Collections.replaceAll(list, 1, 10); ==>{10,10,10,2,3,4,5}
Predicate: can be applied to any collection-Type
number % 2 != 0
Predicate<Ineteger> oddNumber = p -> p %2 != 0;
ArrayLisst method:
remove If(Predicate): removes everything that's matching with the expression of predicatelist of arrays
List<Object[]> list = new ArrayList<>();
list.add(new String[5]);
list.add(new Integer[5]);
Object[] objects = list.get(0);Copyright © 2021 Codeinu
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