Java Code Snippets

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Most of the time some code snippets will be provided to us and we need to figure out the answer. Below are some of the question commonly asked in interviews.

Code	Output	Comment
System.out.print("Amigo"); System.out.println("Is The"); System.out.print("Best");	AmigoIs The Best	println doesn't start printing text from a new line. It prints text on the current line, but makes it so the next text will be printed on a new line.
int a, b, c;		int variables named a, b, c are created. These variables can store integers.
int a = 1 + 'b'; //99 String str = "sss" + a; //sss99		When you add strings and numbers, the result is always a string. We can add character to integer.
String str = "abc" StringBuilder(str).reverse().toString()	cba	Reverse a string using StringBuilder
String str = Arrays.stream(result) .mapToObj(String::valueOf) .collect(Collectors.joining())	For eg str = ['1','2','3'] then result "123" string	Concatenate array values to a String
Difference between int[] arr = new int[]{2,4,6,7,9}; and int[] arr = {2,4,6,7,9};		int[] arr = new int[]{2,4,6,7,9}; This approach combines the array declaration (int[] arr) with initialization using a new keyword (new). It explicitly allocates memory for the array of the specified size (5 elements in this case) and then initializes the elements with the provided values within curly braces {}. int[] arr = {2,4,6,7,9}; This is a shorthand notation for array initialization. Java allows directly initializing the array with values within curly braces {} during declaration. Internally, Java still creates an array and assigns the provided values to its elements. Essentially, both methods achieve the same result
Increment Operator ++i and i++		++i (Pre-increment): The variable is incremented by 1 first. The incremented value is returned and used in the expression. i++ (Post-increment): The current value of the variable is used in the expression first. Then, the variable is incremented by 1.
Return sub-array Arrays.copyOfRange(arr, start, end);		If we want to return a subarray of an int[] array in Java, we can use the Arrays.copyOfRange() method. This method allows you to create a new array that is a copy of a specified range of elements from the original array.
int[] arr = { 1, 2, 1, 3, 5, 1 }; System.out.println(Arrays.toString(arr)); List<Integer> arrList = IntStream.of(arr) .boxed() .collect(Collectors.toList());		To convert int array to ArrayList
int[] result = arrList.stream() .mapToInt(Integer::intValue) .filter(element -> element != key) .toArray();		Convert ArrayList back to int array
for (i = 0;i<10;i++) { System.out.print(i); } System.out.println(); for (i=0;i<10;++i) { System.out.print(i); }	0123456789 0123456789	Both loops will print the same sequence of numbers because the difference between ++i and i++ only matters when the incremented value of i is being used within the same expression.
int i; System.out.print(i);	Compile Error
System.out.println(s1 = "aaa"); // aaa System.out.println(i = 10); // 10		Assignmnet operator while printing is valid
int[] arr = new int[10]; System.out.println(arr);	[I@hashcode (the actual hashcode will vary). This is not the actual content of the array, but a memory address and a hashcode representing the array object itself.	An array in Java is an object. It doesn't have a built-in way to directly print its contents using System.out.println(arr). When you try to print the array itself, Java prints the object representation, which includes:[I: This indicates the array's type. [I signifies an array of integers (int). @: This symbol separates the type information from the hashcode. hashcode: This is a unique identifier generated for the array object itself. It's used for internal memory management purposes.
public static void main(String[] args) { int[] arr = new int[10]; System.out.println(arr[9]); }	0	Array elements are initialized with default 0 value.
public class Application { static ArithmeticException e; public static void main(String[] args) { throw e; } }	NullPointer Exception
public class Application { static ArithmeticException e = new ArithmeticException(); public static void main(String[] args) { throw e; } }	Arithmetic Excpetion
int[] result = {1,2,3}; List<Integer> arrList = IntStream.of(arr) .boxed() .collect(Collectors.toList());		Convert int[] to List<Integer>