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)

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