Java Collections

// Import and create
import java.util.ArrayList;

ArrayList list = new ArrayList<>();  # dynamic array

// Add elements
list.add("Apple");  # add to end
list.add("Banana");

// Access elements
String first = list.get(0);  # get by index

// Remove elements
list.remove(0);  # remove by index
list.remove("Apple");  # remove by value

// Common methods
list.size()  # number of elements
list.isEmpty()  # check if empty
list.contains("Apple")  # check existence
list.clear()  # remove all

// Set element
list.set(0, "Orange");  # replace at index

// Import and create
import java.util.HashMap;

HashMap map = new HashMap<>();  # key-value pairs

// Add key-value pairs
map.put("John", 25);  # insert/update
map.put("Jane", 30);

// Get value
int age = map.get("John");  # returns 25

// Remove entry
map.remove("John");  # delete key-value

// Common methods
map.containsKey("John")  # check if key exists
map.containsValue(25)  # check if value exists
map.size()  # number of pairs
map.isEmpty()
map.clear()

// Get all keys and values
map.keySet()  # all keys
map.values()  # all values

// Import and create
import java.util.HashSet;

HashSet set = new HashSet<>();  # unique elements only

// Add elements
set.add("Apple");
set.add("Banana");
set.add("Apple");  # duplicate ignored

// Remove element
set.remove("Apple");

// For-each loop
for (String item : list) {  # iterate list
    System.out.println(item);
}

// Iterate HashMap
for (String key : map.keySet()) {
    System.out.println(key + ": " + map.get(key));
}

// Import and create
import java.util.LinkedList;

LinkedList list = new LinkedList<>();  # doubly-linked

// Add to front/end
list.addFirst("First");  # add at beginning
list.addLast("Last");  # add at end

// Remove from front/end
list.removeFirst();
list.removeLast();

// Import Collections
import java.util.Collections;

// Sort list
Collections.sort(list);  # ascending order

// Reverse list
Collections.reverse(list);  # reverse order

// Find max/min
Collections.max(list);  # largest element
Collections.min(list);  # smallest element