String Methods

Question 1

Declaring a String

Answer 1

String str = “Welcome”;

Question 2

Find Character at nth position of the string

Answer 2

Char Ch = str.charAt(nth);

Question 3

Convert a String into Char Array

Answer 3

Char[] array = str.toCharArray();

Question 4

Covert a String to Int

Answer 4

Method 1 : Using Integer.parseInt
 String str3="1234";
 int num3 = Integer.parseInt(str3)
==============================
 Method 2: Using Integer.valueOf
 String str="1122";
 int num = Integer.valueOf(str);

Question 5

Convert a int to String

Answer 5

Method 1: Using Integer.toString(int i)
 int ivar2 = 200;
 String str2 = Integer.toString(ivar2);
=================================
 Method 2: Using String.valueOf(int i)
 int ivar = 111;
 String str = String.valueOf(ivar);

Question 6

Convert string to Double

Answer 6

String str3 = 11.22;
Method 1 : Double var = Double.parseDouble(str3);
Method 2 : Double var3 = Double.valueOf(str3);

Question 7

Convert ASCII to Char

Answer 7

I/P - int num[] = {65, 120, 98, 75, 115};
String str1 =null;
String str2 =null;
for(int i: num){
Method 1 -> str1 = Character.toString((char)i);
Method 1 -> str2 = String.valueof(Character.toChar()int);
System.out.print(str+ “ “);
}
O/P - A x b K s

Question 8

Convert Char to ASCII

Answer 8

char character = ‘a’;

int ascii = (int) character;

Question 9

Covert a string to ArrayList

Answer 9

String num = "22,33,44,55,66,77";
 String[] str = num.split(",");
 List arraylist = new ArrayList();
 arraylist = Arrays.asList(str)

Question 10

Find the Length of the string

Answer 10

int Length = str.length();

Question 11

find the index of first occurrence of the specified character ch in the string

Answer 11

int Position = str.indexOf(Char);

Question 12

Add One string to other

Answer 12

String Combined = str1.concat(str2)

Question 13

Splitting the string

Answer 13

Char[] array = str.split(“,or / or any Regex”);

Question 14

Convert All the characters to Upper Case

Answer 14

String newUpper = str.toUpperCase();

Question 15

Convert All the characters to Lower case

Answer 15

String newLower = str.toLowerCase();

Question 16

string matches

Answer 16

Input :
String str = new String(“Java String Methods”);
System.out.print(“Regex: (.)String(.) matches string? “ );
Output: TRUE

Question 17

Equality Check of two strings

Answer 17

stringOne.equal(stringTwo) returns TRUE if matches else false

Question 18

Some basic Validation for String Input Questions (Applies to Most)

Answer 18

1. Is the string null ? -> (input == null)
2. Is the string empty ? -> (input.isEmpty()) or (input.length == 0)
3. Does the string have only one char ? -> (input.length == 1)

Question 19

Whats the difference between string.isEmpty() and string == null?

Answer 19

The empty string is a string with zero length. The null value is not having a string at all.
The expression s == null will return false if s is an empty string.
The second version will throw a NullPointerException if the string is null.
Here’s a table showing the differences:
+——-+———–+———————-+
| s | s == null | s.isEmpty() |
+——-+———–+———————-+
| null | true | NullPointerException |
| “” | false | true |
| “foo” | false | false |
+——-+———–+———————-+