Strings are immutable (cannot change) Strings are objects (not primatives)
// Creation
String s = "Hello, World!";
s = "Change the value";
String s = new String("Hello, World");
// Concatination
s = s + "Addition";Indexes start at 0
| String | H | e | l | l | o |
|---|---|---|---|---|---|
| Index | 0 | 1 | 2 | 3 | 4 |
| Function Name | Parameter List | Return |
|---|---|---|
s.length() |
int: the length of the string |
|
s.substring() |
int start: Start index of your substring int end End index of your substring |
String: A substring of s from indecies start to end - 1 |
s.substring() |
int start: Start index of your substring |
String: A substring for index start to the end of the string |
s.indexOf() |
String str: String to search for within the string |
int: if str is found inside s, then it gives the index where it is found, if not returns -1 |
s.indexOf() |
String str: String to search for within the string int i: Index to start your search |
int: if str is found inside s after index i, then it gives the index where it is found, if not returns -1 |
s.lastIndexOf() |
String str: String to search for within the string |
int: if str is found within s, it gives the index of the last occurence of that str, otherwise returns -1 |
s.charAt() |
int i: Index in the string |
char: Returns the character at index i |
s.compareTo() |
String str: String to compare to |
int: returns the ascii difference between the first different characters going left to right |
s.equals() |
String other: String to compare to |
boolean: true if they are equal to one another, false otherwise. Do NOT use == |
s.equalsIgnoreCase() |
String other: String to compare to |
boolean: true if they are equal to one another, ignoring whether or not the letters are uppercase / lowercase, false otherwise. Do NOT use == |
s.split() |
String regex: String to split by |
String[]: Array with the string broken up by the regex |
s.contains() |
String str: String to check against |
boolean: Whether or not str appears within s |
s.startsWith() |
String str: String to check against |
boolean: Whether or not s starts with str |
s.endsWith() |
String str: String to check against |
boolean: Whether or not s ends with str |
s.repeat() |
int n: Number of times to repeat the String` |
String: String containing n copies of s |
s.strip() |
String: s that has all trailing or leading whitespace |
|
s.stripLeading() |
String: s that has all leading whitespace |
|
s.stripTrailing() |
String: s that has all trailing whitespace |
|
s.toCharArray() |
char[]: Character array of all the characters in the string |
|
s.replace() / s.replaceFirst() |
Both paramters allow use of regex String a or char a: String to search for in s String b or char b: String to replace the first instance with. |
String: String with the first instance of a replaced with b |
s.replaceAll() |
Both paramters allow use of regex String a or char a: String to search for in s String b or char b: String to replace each instance with. |
String: String with all instance of a replaced with b |
s.matches() |
String regex: Regular Expression to check against |
boolean: If String s is valid for regex regex |
s.toUpperCase() |
String: s with all characters converted to uppercase |
|
s.toLowerCase() |
String: s with all characters covnerted to lowercase |
|
s.isEmpty() |
boolean: true if s.length() is 0, otherwise false |
|
s.isBlank() |
boolean: true if s.strip().length() is 0, otherwise false |
String s = "Hello";
out.println(s.length()); // Prints out 5
out.println(s.substring(2, 4)); // Prints out ll
out.println(s.substring(1)); // Prints out ello
out.println(s.indexOf("ll")); // Prints out 2
out.println(s.indexOf("ellooo")); // Prints out -1
out.println(s.indexOf("He", 3)); // Prints out -1
out.println(s.lastIndexOf("l")); // Prints out 3
out.println(s.charAt(3)); // Prints out 3
out.println(s.compareTo("Hello")); // Prints out 0
out.println(s.equals("Hello")); // Prints out true
out.println(s.equals("hello")); // Prints out true
out.println(s == "Hello"); // Prints out false
out.println(s.split("e")); // Prints out ["H", "llo"]
out.println(s.split("")); // Prints out ["H", "e", "l", "l", "o"]
out.println(s.contains("ll")); // Prints out true
out.println(s.startsWith("He")); // Prints out true
out.println(s.endsWith("lo")); // Prints out true
out.println(s.repeat(3)); // Prints out HelloHelloHello
out.println(s.toCharArray()); // Prints out ['H', 'e', 'l', 'l', 'o']
out.println(s.replace("ll", "oo")); // Prints out Heooo
out.println(s.matches(".+")); // Prints out true
out.println(s.toUpperCase()); // Prints out HELLO
out.println(s.toLowerCase()); // Prints out helloString s;
i + ""; // Any number (i) to String
s.charAt(0); // String to char
Integer.parseInt(s); // String to int
Integer.valueOf(s); // String to Integer (class)
String.valueOf(x); // Any primitive (x) to String