- LinkedList, ArrayList
    - add(Element e), add(int idx, Element e), get(int idx)
    - remove(int index)
    - remove(Object o)
- Stack
    - push(E item)
    - peek()
    - pop()
- PriorityQueue
    - peek()
    - poll()
    - default is min-heap
    - PriorityQueue(int initialCapacity, Comparator<? super E> comparator)
    - PriorityQueue(Collection<? extends E> c)
- HashSet, TreeSet
    - add, remove
- HashMap
    - put(K key, V value)
    - get(Object key)
    - keySet()
    - if you try to get something that's not there, will return null

- it.next() - returns value
- it.hasNext() - returns boolean
- it.remove() - removes last returned value

- String.split(" |\.|\?") //split on space, ., and ?
- StringBuilder
    - much faster at concatenating strings
    - thread safe, but slower
    - StringBuilder s = new StringBuilder(CharSequence seq)();
    - s.append("cs3v");
    - s.charAt(int x), s.deleteCharAt(int x), substring
    - s.reverse()
    - Since String is immutable it can safely be shared between many threads
- formatting
    String s = String.format("%d", 3);
    "%05d"   //pad to fill 5 spaces
    "%8.3f" //max number of digits
    "%-d"    //left justify
    "%,d"    //print commas ex. 1,000,000
    | int | double | string |
    |-----|--------|--------|
    | d   | f      | s      |
    new StringBuilder(s).reverse().toString()
    int count = StringUtils.countMatches(s, something);
- integer
    - String toString(int i, int base)
    - int parseInt(String s, int base)
- array
    char[] data = {'a', 'b', 'c'};
    String str = new String(data);

- Arrays.sort(Array a)
- Collections.sort(Collection c), Collections.sort(Collection l, Comparator c)
    - use mergeSort (with insertion sort if very small)
- Collections.reverseOrder() returns comparator opposite of default
class ComparatorTest implements Comparator<String>
    public int compare(String one, String two) //if negative, one comes first
class Test implements Comparable<Object>
    public int compareTo(Object two)