Common Java String Methods

charAt(int index) charAt(int index): Returns the character at the specified index.
```
String str = "Hello";
char ch = str.charAt(1); // 'e'
```

compareTo(String anotherString) compareTo(String anotherString): Compares two strings lexicographically.

String str1 = "apple";
String str2 = "banana";
int result = str1.compareTo(str2); // negative value

compareToIgnoreCase(String anotherString) compareToIgnoreCase(String anotherString): Compares two strings lexicographically, ignoring case differences.
```
String str1 = "hello";
String str2 = "HELLO";
int result = str1.compareToIgnoreCase(str2); // 0
```

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

String str1 = "Hello, ";
String str2 = "World!";
String result = str1.concat(str2); // "Hello, World!"

contains(CharSequence sequence) contains(CharSequence sequence): Returns true if this string contains the specified sequence of char values.
```
String str = "Hello, World!";
boolean contains = str.contains("World"); // true
```
endsWith(String suffix) endsWith(String suffix): Tests if this string ends with the specified suffix.
```
String str = "Hello.txt";
boolean endsWith = str.endsWith(".txt"); // true
```

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

String str1 = "Hello";
String str2 = "Hello";
boolean isEqual = str1.equals(str2); // true

equalsIgnoreCase(String anotherString) equalsIgnoreCase(String anotherString): Compares this string to another string, ignoring case considerations.
```
String str1 = "hello";
String str2 = "HELLO";
boolean isEqual = str1.equalsIgnoreCase(str2); // true
```
indexOf(int ch) indexOf(int ch): Returns the index of the first occurrence of the specified character.
```
String str = "Hello";
int index = str.indexOf('e'); // 1
```
indexOf(String str) indexOf(String str): Returns the index of the first occurrence of the specified substring.
```
String str = "Hello, World!";
int index = str.indexOf("World"); // 7
```

isEmpty() isEmpty(): Returns true if this string is empty.

String str = "";
boolean isEmpty = str.isEmpty(); // true

lastIndexOf(int ch) lastIndexOf(int ch): Returns the index of the last occurrence of the specified character.
```
String str = "Hello, World!";
int lastIndex = str.lastIndexOf('o'); // 8
```
lastIndexOf(String str) lastIndexOf(String str): Returns the index of the last occurrence of the specified substring.
```
String str = "Hello, World! Hello!";
int lastIndex = str.lastIndexOf("Hello"); // 13
```

length() length(): Returns the length of this string.

String str = "Hello";
int length = str.length(); // 5

replace(char oldChar, char newChar) replace(char oldChar, char newChar): Returns a new string resulting from replacing all occurrences of oldChar with newChar.
```
String str = "Hello";
String result = str.replace('l', 'p'); // "Heppo"
```
replace(String target, String replacement) replace(String target, String replacement): Replaces each substring of this string that matches the literal target sequence with the specified literal replacement sequence.
```
String str = "Hello, World!";
String result = str.replace("World", "Java"); // "Hello, Java!"
```

split(String regex) split(String regex): Splits this string around matches of the given regular expression.

String str = "apple,banana,cherry";
String[] fruits = str.split(","); // ["apple", "banana", "cherry"]

startsWith(String prefix) startsWith(String prefix): Tests if this string starts with the specified prefix.
```
String str = "Hello, World!";
boolean startsWith = str.startsWith("Hello"); // true
```
substring(int beginIndex) substring(int beginIndex): Returns a new string that is a substring of this string.
```
String str = "Hello, World!";
String sub = str.substring(7); // "World!"
```