Java Strings Cheat Sheet- A Complete Reference to Java Strings
Are you a Java programmer looking for a quick guide on Java Concepts? If yes, then you must take Strings into your consideration. This Java String cheat sheet is designed for the Java aspirants who have already embarked on their journey to learn Java. So, let’s quickly get started with this Java String Cheat Sheet.
Java String Cheat Sheet
The string is a sequence of characters. But in Java, a string is an object that represents a sequence of characters. The java.lang.String class is used to create a string object.
Creating a String
String in Java is an object that represents a sequence of char values. A String can be created in two ways:
- Using a literal
- Using ‘new’ keyword
String str1 = “Welcome”; // Using literal
String str2 = new String(”Edureka”); // Using new keywordString Pool
Java String pool refers to a collection of Strings that are stored in heap memory. In this, whenever a new object is created, the String pool first checks whether the object is already present in the pool or not.
String str1 = "abc";
String str2 = "abc";
System.out.println(str1 == str2);
System.out.println(str1 == "abc");String Conversions
String to Int Conversion
String str="123";
int inum1 = 100;
int inum2 = Integer.parseInt(str);// Converting a string to intInt to String Conversion
int var = 111;
String str = String.valueOf(var);
System.out.println(555+str); // Conversion of Int to StringString to Double conversion
String str = "100.222";
double dnum = Double.parseDouble(str); //displaying the value of variable dnumDouble to String Conversion
double dnum = 88.9999; //double value
String str = String.valueOf(dnum); //conversion using valueOf() methodImportant Programs
Finding duplicate characters in a String
This program helps you to find out the duplicate characters in a String.
public void countDupChars(String str)
{
//Create a HashMap
Map<Character, Integer> map = new HashMap<Character, Integer>();
//Convert the String to char array
char[] chars = str.toCharArray();
for(Character ch:chars){
if(map.containsKey(ch)){
map.put(ch, map.get(ch)+1);
} else {
map.put(ch, 1);
}
}
Set<Character> keys = map.keySet(); //Obtaining set of keys
public static void main(String a[]){
Details obj = new Details();
System.out.println("String: Edureka");
obj.countDupChars("Edureka");
System.out.println("
String: StringCheatSheet");
obj.countDupChars("StringCheatSheet");
}
}Removing Trailing Spaces of a String
This program tells you how to trim trailing spaces from the string but not leading spaces.
int len = str.length();
for( ; len > 0; len--)
{
if( ! Character.isWhitespace( str.charAt( len - 1)))
break;
}
return str.substring( 0, len);StringJoiner Class
StringJoiner mystring = new StringJoiner("-");
// Passing Hyphen(-) as delimiter
mystring.add("edureka");
// Joining multiple strings by using add() method
mystring.add("YouTube");String reverse using Recursion
class StringReverse
{
/* Function to print reverse of the passed string */
void reverse(String str)
{
if ((str==null)||(str.length() <= 1))
System.out.println(str);
else
{
System.out.print(str.charAt(str.length()-1));
reverse(str.substring(0,str.length()-1));
}
}
/* Driver program to test above function */
public static void main(String[] args){
String str = "Edureka for Java";
StringReverse obj = new StringReverse();
obj.reverse(str);
}
}Reversing a String entered by a user
String str = "Welcome To Edureka";
String[] strArray = str.split(" ");
for (String temp: strArray)
{
System.out.println(temp);
for(int i=0; i<3; i++)
{
char[] s1 = strArray[i].toCharArray();
for (int j = s1.length-1; j>=0; j--)
{
System.out.print(s1[j]);
}String Classes & Interfaces
String vs String Buffer
String Buffer vs String Builder
Now, interfaces that are implemented by String, StringBuffer, and StringBuilder are shown in the below code.
//String implements all the 3 interfaces
public final class String extends Object
implements Serializable, Comparable<String>, CharSequence
//StringBuffer implements Serializable & CharSequence interfaces
public final class StringBuffer extends Object
implements Serializable, CharSequence
//StringBuilder implements Serializable & CharSequence interfaces
public final class StringBuilder extends Object
implements Serializable, CharSequenceString vs StringBuffer vs StringBuilder
In the below code, we will perform concatenation operation with 3 different classes. But, concatenation will happen only with String Buffer and Builder.
class Edureka{
// Concatenates to String
public static void concat1(String s1)
{
s1 = s1 + "edurekablog";
}
// Concatenates to StringBuilder
public static void concat2(StringBuilder s2)
{
s2.append("edurekablog");
}
// Concatenates to StringBuffer
public static void concat3(StringBuffer s3)
{
s3.append("edurekablog");
}
public static void main(String[] args)
{
String s1 = "Andvideos";
concat1(s1); // s1 is not changed
System.out.println("String: " + s1);
StringBuilder s2 = new StringBuilder("Andvideos");
concat2(s2); // s2 is changed
System.out.println("StringBuilder: " + s2);
StringBuffer s3 = new StringBuffer("Andvideos");
concat3(s3); // s3 is changed
System.out.println("StringBuffer: " + s3);
}
}Hence, in the output, s1 will remain unchanged and s2 and s3 will change and concatenation occurs.
String Methods
Few of the most important and frequently used String methods are listed below:
str1==str2 //compares address;
String newStr = str1.equals(str2); //compares the values
String newStr = str1.equalsIgnoreCase() //compares the values ignoring the case
newStr = str1.length() //calculates length
newStr = str1.charAt(i) //extract i'th character
newStr = str1.toUpperCase() //returns string in ALL CAPS
newStr = str1.toLowerCase() //returns string in ALL LOWERCASE
newStr = str1.replace(oldVal, newVal) //search and replace
newStr = str1.trim() //trims surrounding whitespace
newStr = str1.contains("value"); //check for the values
newStr = str1.toCharArray(); // convert String to character type array
newStr = str1.IsEmpty(); //Check for empty String
newStr = str1.endsWith(); //Checks if string ends with the given suffixImmutable Strings
In Java, string objects are immutable. Immutable simply means unmodifiable or unchangeable.
class Stringimmutable{
public static void main(String args[]){
String s="JavaStrings";
s.concat(" CheatSheet");
System.out.println(s);
}
}The output will be JavaStrings because strings are immutable and the value will not be changed.
With this, we come to an end of Java String Cheat Sheet.
If you wish to check out more articles on the market’s most trending technologies like Artificial Intelligence, DevOps, Ethical Hacking, then you can refer to Edureka’s official site.
Do look out for other articles in this series which will explain the various other aspects of Java.
1. Object Oriented Programming
5. Java String
6. Java Array
8. Java Threads
9. Introduction to Java Servlets
11. Exception Handling in Java
14. Java Programs
15. Kotlin vs Java
16. Dependency Injection Using Spring Boot
22. Socket Programming In Java
25. Library Management System Project in Java
26. Trees in Java
28. Top Data Structures & Algorithms in Java
30. Top 55 Servlet Interview Questions
32. Java Tutorial
34. Java Collections Interview Questions and Answers
35. How to Handle Deadlock in Java?
36. Top 50 Java Collections Interview Questions You Need to Know
37. What is the concept of String Pool in Java?
38. What is the difference between C, C++, and Java?
39. Palindrome in Java- How to check a number or string?
40. Top MVC Interview Questions and Answers You Need to Know
41. Top 10 Applications of Java Programming Language
42. Deadlock in Java
43. Square and Square Root in Java
Originally published at https://www.edureka.co.
