Java Tutorial for Beginners 2023 | String Methods in Java | Java String Class | Parnika Tutorials

"Java Tutorial for Beginners 2023 | String Methods in Java | Java String Class | Parnika Tutorials
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00:00 - Introduction
00:39 - What is a String
01:28 - How to declare a string
05:39- String methods
46:40 - Implementation of string methods
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String is a sequence of characters. In java, objects of String are immutable which means a constant and cannot be changed once created.

Creating a String

There are two ways to create string in Java:

String literal

String s = “GeeksforGeeks”;

Using new keyword

String s = new String (“GeeksforGeeks”);
String Methods

int length(): Returns the number of characters in the String.

"GeeksforGeeks".length(); // returns 13

Char charAt(int i): Returns the character at ith index.

"GeeksforGeeks".charAt(3); // returns ‘k’

String substring (int i): Return the substring from the ith index character to end.

"GeeksforGeeks".substring(3); // returns “ksforGeeks”

String substring (int i, int j): Returns the substring from i to j-1 index.

"GeeksforGeeks".substring(2, 5); // returns “eks”

String concat( String str): Concatenates specified string to the end of this string.

String s1 = ”Geeks”;
String s2 = ”forGeeks”;
String output = s1.concat(s2); // returns “GeeksforGeeks”

int indexOf (String s): Returns the index within the string of the first occurrence of the specified string.

String s = ”Learn Share Learn”;
int output = s.indexOf(“Share”); // returns 6

int indexOf (String s, int i): Returns the index within the string of the first occurrence of the specified string, starting at the specified index.

String s = ”Learn Share Learn”;
int output = s.indexOf("ea",3);// returns 13

Int lastIndexOf( String s): Returns the index within the string of the last occurrence of the specified string.

String s = ”Learn Share Learn”;
int output = s.lastIndexOf("a"); // returns 14

boolean equals( Object otherObj): Compares this string to the specified object.

Boolean out = “Geeks”.equals(“Geeks”); // returns true
Boolean out = “Geeks”.equals(“geeks”); // returns false

boolean equalsIgnoreCase (String anotherString): Compares string to another string, ignoring case considerations.

Boolean out= “Geeks”.equalsIgnoreCase(“Geeks”); // returns true
Boolean out = “Geeks”.equalsIgnoreCase(“geeks”); // returns true

int compareTo( String anotherString): Compares two string lexicographically.

int out = s1.compareTo(s2); // where s1 ans s2 are
// strings to be compared

This returns difference s1-s2. If :
out -ve // s1 comes before s2
out = 0 // s1 and s2 are equal.
out +ve // s1 comes after s2.

int compareToIgnoreCase( String anotherString): Compares two string lexicographically, ignoring case considerations.

int out = s1.compareToIgnoreCase(s2);
String toLowerCase(): Converts all the characters in the String to lower case.

String word1 = “HeLLo”;
String word3 = word1.toLowerCase(); // returns “hello"

String toUpperCase(): Converts all the characters in the String to upper case.

String word1 = “HeLLo”;
String word2 = word1.toUpperCase(); // returns “HELLO”

String trim(): Returns the copy of the String, by removing whitespaces at both ends. It does not affect whitespaces in the middle.