Java String API Cheatsheet

Create a String

String string = "One Compiler";                 // Using literal
String string2 = new String("One Compiler");     // Using new Keyword

char[] characters = {'a', 'b', 'c', 'd'};
String string3 = new String(characters);         //Gives output as "abcd" 

byte[] characters = {65, 66, 67, 68};
String string3 = new String(characters);         //Gives output as "ABCD" 

String Comparison

String string = "One Compiler";                 
String string2 = new String("One Compiler");     

// Following methods returns boolean value.
string == string2;                  // (==) Compares address of the values
string.equals(string2)              // (equals) Compares the actual values
string.equalsIgnoreCase(string2)    // (equalsIgnoreCase) Compares values and also ignores case
string.contentEquals(string2)       // (contentEquals) Checks for same Sequence of characters values against the other string

//Following methods return int value
string.compareToIgnoreCase(string2)  // (compareToIgnoreCase) Returns 0 if values are equal ignoring case, Returns < 0 if the string is lexicographically less than the other string, Returns > 0 if the string is lexicographically greater than the other string
string.compareTo(string1)            // (compareTo) Returns 0 if values are equal, Returns < 0 if the string is lexicographically less than the other string, Returns > 0 if the string is lexicographically greater than the other string

concat(): Append two strings

String string = "Welcome to ";  
String string1 = "One Compiler"; 
string.concat(string1) // returns Welcome to One Compiler

contains(): Checks whether string contains given value or not and return boolean value

String string = "One Compiler"; 
string.contains("One")  //returns true

join(): Returns a combined string with given values/array and specified delimiter in between.

String.join(",", "audi", "bmw", "cadillac", "kwid")  //returns audi,bmw,cadillac,kwid
String[] array = {"Welcome", "to", "One", "Compiler"};
String.join("-",array);       //returns Welcome-to-One-Compiler

length(): Returns the length of the string.

String string = "One Compiler"; 
string.length()   //returns 12

indexOf(): Returns the first occurrence of specified character in given string

String string = "One Compiler";
string.indexOf("C");  //returns 4

lastIndexOf(): Returns the last occurrence of specified character in a given string

String string = "One Compiler";
string.lastIndexOf("e");  //returns 10

replace(): Replaces all the occurrences of specified character/charsequence with given character/charsequence.

String string = "One Compiler";
string.replace("e", "r");  //returns Onr Compilrr

replaceAll(): Replaces all the occurrences matching specified regex with given string.

String string = "One Compiler";
string.replaceAll("\\s", "");  //returns OneCompiler

split(): Returns char array by splitting given string based on given regex.

String string = "Welcome to One Compiler";
String[] splitArray = string.split("\\s");
for(String word : splitArray) {  
    System.out.println(word);   
}

output:
Welcome
to
One
Compiler

split(): Returns char array by splitting given string based on given regex and specified split limit.

String string = "Welcome to One Compiler";
String[] splitArray = string.split("\\s", 2);
for(String word : splitArray) {  
    System.out.println(word);   
}

output:
Welcome
to One Compiler

hashCode(): Returns the hashCode of given string

String string = "One Compiler";
string.hashCode();  //returns 599566681

isEmpty(): Returns boolean value, returns true when given string is empty else returns false

String string = "";
string.isEmpty();  //returns true

String string = "one";
string.isEmpty();  //returns false

String string = null;
string.isEmpty();  //throws java.lang.NullPointerException

codePointAt(): Returns unicode of the character of the specified index

String string = "One Compiler"; 
string.codePointAt(1)   //returns 110

charAt(): Returns the character of the specified index

String string = "One Compiler";
string.charAt(5) //returns o

codePointBefore(): Returns the unicode of the character before specified index

String string = "One Compiler";
string.codePointBefore(5) //returns 67

codePointCount(): It accepts two parameters i.e., startIndex and endIndex and returns the number unicode values found between two specified indexes.

String string = " o n e compiler";
string.codePointCount(0, 5) //returns 5

copyValueOf(): Returns string from the array of characters

char[] characters = {'a', 'q', 'c', 'i', 'r', 'w'};
String string = "";
string.copyValueOf(characters, 0, 3); // returns "aqc"

valueOf(): It converts different types of values into string

endsWith(): Returns true if string ends with given value else returns false

String string = "One Compiler";
string.endsWith("ler") //returns true
string.endsWith("sss") //returns false

startsWith(): Returns true if string starts with given value else returns false

String string = "One Compiler";
string.startsWith("One") //returns true
string.startsWith("sss") //returns false

startsWith(String prefix, int offset): Returns true if string starts with given prefix index starting with offset else returns false

String string = "One Compiler";
string.startsWith("One", 0) //returns true
string.startsWith("One", 2) //returns false

substring(int beginIndex): Returns characters from a string from specified index

String string = "One Compiler";
string.substring(2);  //returns e Compiler

substring(int beginIndex, int endIndex): Returns characters from a string between specified start and end indexes

String string = "One Compiler";
string.substring(4, 8);  //returns Comp

toCharArray(): Returns char array of the string.

String string = "One";
for(Character s : string.toCharArray()) {
    System.out.println(s);
}

output:
O
n
e

toLowerCase(): Returns given string in lower case

String string = "One Compiler";
string.toLowerCase();  //returns one compiler

toUpperCase(): Returns given string in upper case

String string = "One Compiler";
string.toUpperCase();  //returns ONE COMPILER

trim(): Returns string by removing leading and trailing spaces i.e., It removes unicode value '\u0020' from a beginning and ending of a given string

String string = "  One Compiler";
string.trim();  //returns One Compiler

Java 8 Streams of string join/append

Collectors.joining(): Returns a concatenated string from stream
Collectors.joining(CharSequence delimiter): Returns a concatenated string separated by delimiter
Collectors.joining(CharSequence delimiter, CharSequence prefix, CharSequence suffix ): Returns a concatinated string separated by delimiter as well as appending specified prefix and suffix

Stream<String> stream = Arrays.asList("audi", "bmw", "cadillac", "dodge").stream();  
String string = stream.collect(Collectors.joining());    //Returns audibmwcadillacdodge   
string = stream.collect(Collectors.joining(","));      //audi,bmw,cadillac,dodge
string = words.collect(Collectors.joining(",", "{", "}"));    //{audi,bmw,cadillac,dodge} 

Java 11 String API Additions

repeat(): Repeats the string content

String string = "Ra ".repeat(2) + "Ramone";
System.out.println(string);

output:
Ra Ra Ramone

strip(): Returns a string with all leading and trailing whitespaces removed

System.out.println(("\n\t  hi   \u2005".strip()));

output:
hi

isBlank(): Returns true if the string is empty or contains only whitespace. Otherwise, it returns false

System.out.println(("\n\t\u2005  ".isBlank()));

output:
true

lines(): Returns a Stream of lines extracted from the string, separated by line terminators

String multilineStr = "This is\n \n a practice\n line.";
long lineCount = multilineStr.lines().count();
System.out.println(lineCount);

output:
4