| Mathematical Operators | Symbol | Meaning | Example |
|---|---|---|---|
| + | addition | 4 + 5 = 9 | |
| - | subtraction | 9 - 5 = 4 | |
| * | multiplication | 3*5 = 15 | |
| / | division | 6/3 = 2 6/4 = 1 6.0/4 = 1.5 | |
| % | mod/remainder | 5 % 3 = 2 | |
| String Operators | + | concatenation | "ab"+"cd"="abcd" |
| Primitive Comparison Operators | == | is equal to | 3 == 3 is true |
| != | is not equal to | 3 != 3 is false | |
| >= | is greater than or equal to | 4 >= 3 is true | |
| <= | is less than or equal to | 4 <= 3 is false | |
| > | is strictly greater than | 4 > 3 is true | |
| < | is strictly less than | 3 < 3 is false
| |
| Boolean Operators | |||
x=5 | ! | flips the value of a boolean | !(x == 5) is false |
| && | returns true only if both parts of it are true
| (x > 3 && x < 7) is true(x > 3 and x > 7) is false | |
| || | returns true if at least one part of it is true
| (x < 3 || x > 7) is false(x < 3 || x < 7) is true | |
| Object Comparison Methods | |||
| equals(Object other) | indicates whether some other object is "equal to" this one | ||
| compareTo(Object other) | Returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified other object. | ||
| compare(Object o1, Object o2) | Compares its two arguments for order. | ||
| String Methods | |||
s="colorful" | Name | Returns | Example |
| .indexOf(String str) | index of first occurrence | s.indexOf("o") == 1 s.indexOf("e") == -1 | |
| .indexOf(String str, int fromIndex) | index of first occurrence starting at the specified index | s.indexOf("o",2) == 3 | |
| .substring(int beginIndex, int endIndex) | Returns a new string that begins at the specified beginIndex and extends to the character at index endIndex - 1 | s.indexOf("1,3").equals("ol") | |
| .trim() | copy with leading/trailing whitespace removed | " big ".trim().equals("big") | |
| .split(String regex) | Splits this string around matches of the given regular expression and return an array. | "big bad dog".split(" ") is {"big","bad", "dog"} "this,old,man".split(",") is {"this", "old", "man"} | |
| In general can split on any other strings, not just a comma, e.g., s.split(":") will split on a colon, s.plot("\\s+") will split on all white space, and s.split("gat") will split on the string "gat". | |||
| .startsWith(String str) | boolean if starts with string | s.startsWith("color") == trues.startsWith("cool") == false
| |
| Type Conversion Functions | |||
| (int)x | turn x into an int value if x is a double, long, char, etc. | (int) 123.99 == 123 | |
| Integer.parseInt(String s) | turns String into an int value. | Integer.parseInt("1024") == 1024 | |
| Integer.toString(int n) | turn n into a String | Integer.toString(-70).equals("-70") | |
| Similar methods exist for double (Double), char (Character), long (Long) | |||
| Random Methods | Math.random() | returns a random value in the range [0.0, 1.0) | |
| nextInt(int n) | Returns a random integer between 0 and n-1 inclusive. | Random gen = new Random(); // produces a number between 0 and 9 gen.nextInt(10); | .
|
| nextDouble() | Returns a random real number between 0 and 1. | ||
| Scanner Methods | |||
| .clear() | close the scanner | ||
| .hasNext() | returns true if the scanner has another token | ||
| .hasNextDouble() | returns true if the next token in the scanner's input can be interpreted as a double | ||
| .hasNextInt() | returns true if the next token in the scanner's input can be interpreted as an int | ||
| .next() | finds and returns the next complete token (string) | ||
| .next(pattern) | returns the next token if it matches the specified pattern | ||
| .nextInt() | returns the next token of the input as an int | ||
| .useDelimiter(pattern) | sets the scanner's delimiting pattern to the specified pattern | ||
| ArrayList Methods | |||
| .add(element) | add a specified element to the end of the list | ||
| .clear() | removes all of the elements in the list | ||
| .contains(object) | returns true if the list contains the specified object | ||
| .get(index) | returns the element at the specified index of the list | ||
| .isEmpty() | returns true if the list is empty | ||
| .remove(object) | removes the first occurrence of the specified object from the list, if present | ||
| .size() | returns the number of elements in the list | ||
| .toArray(T[] a) | converts the ArrayList into an array, e.g. String[] array = list.toArray(new String[0]); | ||
| LinkedList Methods | |||
| .add(element) | appends the element to the end of the list | ||
| .peek() | retrieves but does not remove the head (first element) of the list | ||
| .poll() | retrieves and removes the head of the list | ||
| Set Methods | .add(element) | adds an element to the set if it is not already present | |
| .addAll(Collection c) | adds all of the elements of specified collection to the set if it is not already present | ||
| .contains(object) | returns true if the set contains the specified object | ||
| .isEmpty() | returns true if the set is empty | ||
| .remove(object) | removes the specified object from the set if present | ||
| .removeAll(Collection c) | removes from this set all of the elements from the specified collection if present | ||
| .retainAll(Collection c) | Retains only the elements from the specified collection if present | ||
| Map Methods | |||
| .clear() | Removes all mappings from this map. | ||
| .containsKey(key) | returns true if this map contains a mapping for the specified key. | ||
| .containsValue(value) | returns true if this map maps some key to the specified value. | ||
| .entrySet() | returns a set of Map.Entry pairs (key and value). | ||
| .get(key) | returns the value that the specified key is associated with | ||
| .isEmpty() | returns true if the map is empty | ||
| .keySet() | returns a set of the keys in the map | ||
| .put(key, value) | associated the specified key with the specified value in the map | ||
| .remove(key) | remove the mapping for this key | ||
| .size() | returns the number of mappings | ||
| .values() | returns a Collection of the values contained in the map | ||
| Collections Methods | |||
| Collections.sort(list) | sorts the list in the ascending order | ||
| Collections.sort(list, comparator) | sorts the list according to the order induced by the comparator (e.g., List | ||
| Queue Methods | |||
| .add(element) | add a specified element to the queue | ||
| .peek() | retrieves, but does not remove, the head (oldest element added) of this queue | ||
| .poll() | retrieves and removes the head of this queue | ||
| Priority Queue | |||
| PriorityQueue() | creates a PriorityQueue and orders its elements according to their natural ordering. | ||
| PriorityQueue(initialCapacity, Comparator) | creates a PriorityQueue with the specificed initial capacity and orders its elements according to the comparator | ||
| .add(element) | add a specified element to the queue | ||
| .clear() | removes all the elements from the queue | ||
| .peek() | retrieves, but does not remove, the head of this queue | ||
| .poll() | retrieves and removes the head of this queue | ||
| .size() | returns the number of elements in this queue | ||
| Stack Methods | |||
| .empty() | tests if the stack is empty | ||
| .peek() | retrieves, but does not remove, the top (element added most recently) of the stack | ||
| .pop() | retrieves and removes the top of the stack | ||
| .push(item) | pushes the item onto the top of the list | ||