Java Methods Cheat Sheet SDET

If you’re using Java for Test Automation, this cheat sheet will definitely be helpful.

Essential Java Methods for SDETs

Category	Method	Usage	Example
String Handling	`String.equals()`	Compares two strings for equality.	`"abc".equals("abc") // true`
	`String.contains()`	Checks if a string contains a specific sequence of characters.	`"automation".contains("auto") // true`
	`String.substring()`	Extracts a portion of a string.	`"SDET".substring(1, 3) // "DE"`
	`String.split()`	Splits a string into an array based on a delimiter.	`"A,B,C".split(",") // ["A", "B", "C"]`
	`String.replace()`	Replaces all occurrences of a character or substring.	`"test".replace("t", "T") // "TesT"`
	`String.trim()`	Removes whitespace from both ends of a string.	`" test ".trim() // "test"`
	`String.toLowerCase()`	Converts a string to lowercase.	`"AUTOMATION".toLowerCase() // "automation"`
	`String.toUpperCase()`	Converts a string to uppercase.	`"automation".toUpperCase() // "AUTOMATION"`
	`String.isEmpty()`	Checks if a string is empty.	`"".isEmpty() // true`
	`String.valueOf()`	Converts other data types to a string.	`String.valueOf(123) // "123"`
Collections	`List.add()`	Adds an element to a list.	`list.add("item")`
	`List.remove()`	Removes an element from a list by index or value.	`list.remove(0)`
	`List.get()`	Retrieves an element by index.	`list.get(1)`
	`List.size()`	Returns the size of the list.	`list.size() // 3`
	`Set.add()`	Adds an element to a set (ignores duplicates).	`set.add("item")`
	`Set.contains()`	Checks if a set contains an element.	`set.contains("item") // true`
	`Map.put()`	Adds or updates a key-value pair in a map.	`map.put("key", "value")`
	`Map.get()`	Retrieves a value by key from a map.	`map.get("key") // "value"`
	`Map.containsKey()`	Checks if a map contains a specific key.	`map.containsKey("key") // true`
	`Map.keySet()`	Returns a set of all keys in a map.	`map.keySet() // ["key1", "key2"]`
	`Collections.sort()`	Sorts a list of elements.	`Collections.sort(list)`
	`Collections.reverse()`	Reverses the order of a list.	`Collections.reverse(list)`
	`Arrays.asList()`	Converts an array to a list.	`Arrays.asList(1, 2, 3) // [1, 2, 3]`
	`Arrays.sort()`	Sorts an array of elements.	`Arrays.sort(array)`
File Handling	`Files.readAllLines()`	Reads all lines of a file into a list.	`Files.readAllLines(Paths.get("file.txt"))`
	`Files.write()`	Writes data to a file.	`Files.write(Paths.get("file.txt"), "data".getBytes())`
	`File.exists()`	Checks if a file exists.	`new File("file.txt").exists() // true`
	`File.mkdir()`	Creates a new directory.	`new File("dir").mkdir()`
	`File.delete()`	Deletes a file or directory.	`new File("file.txt").delete()`
	`BufferedReader.readLine()`	Reads a single line from a file.	`bufferedReader.readLine()`
Date & Time	`LocalDate.now()`	Gets the current date.	`LocalDate.now() // 2024-12-12`
	`LocalTime.now()`	Gets the current time.	`LocalTime.now() // 14:30:00`
	`LocalDateTime.now()`	Gets the current date and time.	`LocalDateTime.now() // 2024-12-12T14:30:00`
	`DateTimeFormatter.ofPattern()`	Formats a date or time in a specific pattern.	`DateTimeFormatter.ofPattern("yyyy-MM-dd").format(LocalDate.now()) // "2024-12-12"`
	`Duration.between()`	Calculates the duration between two time points.	`Duration.between(start, end).toMinutes() // 10`
	`ChronoUnit.DAYS.between()`	Calculates the number of days between two dates.	`ChronoUnit.DAYS.between(date1, date2) // 5`
Math & Numbers	`Math.max()`	Returns the larger of two numbers.	`Math.max(10, 20) // 20`
	`Math.min()`	Returns the smaller of two numbers.	`Math.min(10, 20) // 10`
	`Math.pow()`	Raises a number to the power of another.	`Math.pow(2, 3) // 8.0`
	`Math.sqrt()`	Returns the square root of a number.	`Math.sqrt(16) // 4.0`
	`Integer.parseInt()`	Converts a string to an integer.	`Integer.parseInt("123") // 123`
	`Double.parseDouble()`	Converts a string to a double.	`Double.parseDouble("123.45") // 123.45`
Assertions	`Assert.assertEquals()`	Asserts that two values are equal (JUnit/TestNG).	`Assert.assertEquals(actual, expected)`
	`Assert.assertTrue()`	Asserts that a condition is true.	`Assert.assertTrue(value > 0)`
	`Assert.assertFalse()`	Asserts that a condition is false.	`Assert.assertFalse(value < 0)`
	`Assert.assertNotNull()`	Asserts that an object is not null.	`Assert.assertNotNull(object)`
System Operations	`System.out.println()`	Prints data to the console.	`System.out.println("Hello, SDET!")`
	`System.currentTimeMillis()`	Returns the current time in milliseconds.	`System.currentTimeMillis()`
	`System.getenv()`	Retrieves environment variables.	`System.getenv("PATH")`
Regular Expressions	`Pattern.compile()`	Compiles a regular expression into a pattern.	`Pattern.compile("[0-9]+")`
	`Matcher.find()`	Checks if the pattern matches a substring.	`matcher.find() // true`
	`Matcher.group()`	Retrieves matched groups from a regex pattern.	`matcher.group() // "123"`
	`String.matches()`	Checks if a string matches a regex.	`"12345".matches("\\d+") // true`
Threading	`Thread.sleep()`	Pauses execution for a specified time.	`Thread.sleep(1000)`
	`ExecutorService.submit()`	Submits a task for execution in a thread pool.	`executorService.submit(task)`

Essential Java Methods for SDETs

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