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Dictionary
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Java Dictionary
| Beginners Guide: Overview, Features, and Learning Path | An overview of Java, Write Once Run Anywhere, static typing, how execution works (.java → javac → .class → JVM), and a recommended learning path through this dictionary. |
| Comments (// and /* */ and /** */) | Comment syntax in // / /* */ / /** */, when to write comments, and when not to. |
| [Setup] Java Development Environment | Setup instructions for installing, compiling, and running Java. |
| Creating and Running .java Files | How to write, compile, and run .java files. |
| String.length() / charAt() | Gets the length of a string and retrieves a character at a specific position. |
| String.indexOf() / lastIndexOf() / contains() | Searches for a substring and checks its existence. |
| String.startsWith() / endsWith() / matches() | Checks prefix, suffix, and regular expression matching. |
| String.substring() | Extracts a portion of a string. |
| String.replace() / replaceAll() / replaceFirst() | Replaces parts of a string. |
| String.toUpperCase() / toLowerCase() / trim() | Converts case and removes whitespace. |
| String.split() / String.join() | Splits and joins strings. |
| String.equals() / equalsIgnoreCase() / compareTo() | Compares strings. |
| String.valueOf() / Integer.toString() | Converts between numbers and strings. |
| String.toCharArray() / String.copyValueOf() | Converts between a string and a character array. |
| new StringBuilder() / builder.append() / insert() | Mutable string operations for appending and inserting. |
| builder.reverse() / replace() / toString() | Reverses, replaces, and converts strings. |
| Arrays.sort() / Arrays.binarySearch() | Sorts an array and performs binary search. |
| Arrays.copyOf() / Arrays.copyOfRange() / Arrays.fill() | Copies and fills arrays. |
| Arrays.equals() / Arrays.toString() / Arrays.asList() | Compares arrays, converts to string, and converts to List. |
| new ArrayList<>() / list.add() / set() / get() | Creates a list, and adds, updates, and retrieves elements. |
| list.remove() / clear() / size() / isEmpty() | Removes elements, clears a list, and checks its size. |
| list.contains() / indexOf() / subList() | Searches within a list and retrieves a sublist. |
| Collections.sort() / Collections.shuffle() / Collections.reverse() | Sorts, shuffles, and reverses a list. |
| new HashMap<>() / map.put() / get() / getOrDefault() | Creates a map, and adds and retrieves entries. |
| map.remove() / containsKey() / containsValue() / size() | Removes entries and checks for key existence. |
| map.keySet() / values() / entrySet() | Retrieves keys, values, and entries from a map. |
| new HashSet<>() / set.add() / contains() / remove() | Creates a set, and adds, checks, and removes elements. |
| set.size() / isEmpty() / iterator() | Gets the size of a set and iterates over it. |
| new LinkedList<>() / queue.offer() / poll() / peek() | Operations on a queue. |
| new ArrayDeque<>() / deque.push() / pop() | Operations on a stack and double-ended queue. |
| collection.stream() / stream.filter() / map() | Creates a stream and filters or transforms its elements. |
| stream.collect() / toList() | Collects a stream into a collection. |
| stream.forEach() / reduce() / count() | Iterates over, aggregates, and counts stream elements. |
| stream.sorted() / distinct() / limit() / skip() | Sorts, removes duplicates, and limits stream elements. |
| stream.findFirst() / anyMatch() / allMatch() / noneMatch() | Searches and evaluates conditions on stream elements. |
| Optional.of() / isPresent() / orElse() / orElseThrow() | A null-safe wrapper class. |
| Integer.parseInt() / Double.parseDouble() | Converts a string to a numeric value. |
| Integer.MAX_VALUE / MIN_VALUE / Integer.toBinaryString() | Integer constants and radix conversion. |
| Math.abs() / max() / min() / round() / floor() / ceil() | Performs numerical calculations and rounding. |
| LocalDate.now() / of() / getYear() / getMonth() | Gets or creates a date. |
| LocalDateTime.now() / LocalTime.now() | Gets the current date, time, or datetime. |
| DateTimeFormatter.ofPattern() / date.format() | Formats and parses date and time values. |
| new Scanner() / scanner.nextLine() / nextInt() | Reads from standard input, strings, and numbers. |
| new BufferedReader() / reader.readLine() | Reads input with buffering. |
| Files.readString() / Files.readAllLines() | Reads the entire content of a file. |
| Files.writeString() / Files.write() | Writes content to a file. |
| Files.exists() / isFile() / isDirectory() / createDirectory() | Checks and creates files and directories. |
| Files.copy() / move() / list() / walk() | Copies, moves, and lists files. |
| Pattern.compile() / Matcher.matches() / find() | Compiles a regular expression and performs matching. |
| Matcher.replaceAll() / replaceFirst() | Replaces text using a regular expression. |
| try / catch / finally / throw | The basic syntax for exception handling. |
| try-with-resources / AutoCloseable | Automatically closes resources. |
| class / new / Constructor / this | Defines a class and creates an instance. |
| public / private / protected / static / final | Access modifiers, static members, and constants. |
| extends / super / @Override | Inheritance and method overriding. |
| interface / implements / abstract | Interfaces and abstract classes. |
| Objects.equals() / Objects.toString() / Objects.requireNonNull() | The Objects utility class. |
| Generics (<T>) | Defines classes and methods with type parameters. |
| Lambda Expressions / (x) -> x * 2 | A concise syntax for anonymous functions. |
| Predicate / Function / Consumer / Supplier | Major functional interfaces. |
| enum | Defines and uses enumeration types. |
| record | An immutable data class. |
| new Thread() / thread.start() / Runnable | Creates and starts a thread. |
| ExecutorService / Executors.newFixedThreadPool() | Executes tasks using a thread pool. |
| CompletableFuture.supplyAsync() / thenApply() / join() | Asynchronous processing. |
| System.out.println() / System.err.println() / System.in | Standard output, error output, and standard input. |
| System.currentTimeMillis() / System.nanoTime() / System.exit() | Time measurement and process termination. |
| Objects.toString() / getClass() / instanceof | Checks the type of an object and converts it to a string. |
| Array Basics (Java) | Fixed-length arrays in Java; covers declaration, initialization, element access, multi-dimensional arrays, and when to use ArrayList instead. |
| final (Java) | The final keyword makes variables non-reassignable, methods non-overridable, and classes non-inheritable in Java. |
| for Loop (Java) | The for loop combining initialization, condition, and update; covers counting, break, continue, and labeled nested loops. |
| Enhanced for / for-each (Java) | The enhanced for statement that iterates over arrays and Iterable collections concisely without an index variable. |
| if / else if / else (Java) | The basic conditional branching syntax in Java. |
| import Statement (Java) | The import statement for using classes and interfaces; covers individual, wildcard, and static imports. |
| main Method / static (Java) | The public static void main(String[] args) entry point and how static methods and fields work in Java. |
| Operators (Java) | Arithmetic, comparison, and logical operators; covers integer division truncation, the + operator for strings, and short-circuit evaluation. |
| Primitive Types (Java) | The eight primitive types that store values directly on the stack; covers bit size, value range, wrapper classes, and type conversion. |
| return / void (Java) | Declaring return types, returning values with return, early exit in void methods, and returning multiple values. |
| switch Statement / switch Expression (Java) | The switch statement and the switch expression finalized in Java 14; covers strings, enums, and returning values with yield. |
| Ternary Operator (Java) | Writes if/else as a one-liner with condition ? true_value : false_value; covers type constraints and readability of nesting. |
| var (Local Variable Type Inference) (Java) | var added in Java 10 lets the compiler infer the local variable type from the right-hand side; not usable for fields, parameters, or return types. |
| while / do-while (Java) | The while loop that repeats while true and do-while that always runs once first; covers infinite loops and input-loop patterns. |
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