arraylist
How to remove specific object from ArrayList in Java?
ArrayList removes objects based on the equals(Object obj) method. So you should implement properly this method. Something like: public boolean equals(Object obj) { if (obj == null) return false; if (obj == this) return true; if (!(obj instanceof ArrayTest)) return false; ArrayTest o = (ArrayTest) obj; return o.i == this.i; } Or public boolean equals(Object … Read more
Print an ArrayList with a for-each loop
Your code works. If you don’t have any output, you may have “forgotten” to add some values to the list: // add values list.add(“one”); list.add(“two”); // your code for (String object: list) { System.out.println(object); }
How to create an 2D ArrayList in java? [duplicate]
I want to create a 2D array that each cell is an ArrayList! If you want to create a 2D array of ArrayList.Then you can do this : ArrayList[][] table = new ArrayList[10][10]; table[0][0] = new ArrayList(); // add another ArrayList object to [0,0] table[0][0].add(); // add object to that ArrayList
Does the capacity of ArrayList decrease when we remove elements?
It doesn’t decrease this automatically. From the doc. public void trimToSize() Trims the capacity of this ArrayList instance to be the list’s current size. An application can use this operation to minimize the storage of an ArrayList instance.
How to append elements at the end of ArrayList in Java?
Here is the syntax, along with some other methods you might find useful: //add to the end of the list stringList.add(random); //add to the beginning of the list stringList.add(0, random); //replace the element at index 4 with random stringList.set(4, random); //remove the element at index 5 stringList.remove(5); //remove all elements from the list stringList.clear();
Java Generic with ArrayList
ArrayList<? extends A> means an ArrayList of some unknown type that extends A. That type might not be C, so you can’t add a C to the ArrayList. In fact, since you don’t know what the ArrayList is supposed to contain, you can’t add anything to the ArrayList. If you want an ArrayList that can … Read more
Why does arraylist class implement List as well as extend AbstractList?
Then wouldn’t it be redundant to implement List as well as extend AbstractList? Yes, it is 100% redundant. However, Java implementors added interfaces very consistently in all public implementation of the collections library: LinkedList<E> and ArrayList<E> extend AbstractList<E> which implements List<E>, and then implement List<E> themselves. HashSet<E> and TreeSet<E> extend AbstractSet<E> which implements Set<E>, and … Read more
Java 8 lambda create list of Strings from list of custom class objects
You need to collect your Stream into a List: List<String> adresses = users.stream() .map(User::getAdress) .collect(Collectors.toList()); For more information on the different Collectors visit the documentation. User::getAdress is just another form of writing (User user) -> user.getAdress() which could as well be written as user -> user.getAdress() (because the type User will be inferred by the … Read more