In Java, string is basically an object that represents sequence of char values. An array of characters works same as Java string. For example: Show
is same as: Java String class provides a lot of methods to perform operations on strings such as compare(), concat(), equals(), split(), length(), replace(), compareTo(), intern(), substring() etc. The java.lang.String class implements Serializable, Comparable and CharSequence interfaces.  CharSequence InterfaceThe CharSequence interface is used to represent the sequence of characters. String, StringBuffer and StringBuilder classes implement it. It means, we can create strings in Java by using these three classes. The Java String is immutable which means it cannot be changed. Whenever we change any string, a new instance is created. For mutable strings, you can use StringBuffer and StringBuilder classes. We will discuss immutable string later. Let's first understand what String in Java is and how to create the String object. What is String in Java?Generally, String is a sequence of characters. But in Java, string is an object that represents a sequence of characters. The java.lang.String class is used to create a string object. How to create a string object?There are two ways to create String object:
1) String LiteralJava String literal is created by using double quotes. For Example: Each time you create a string literal, the JVM checks the "string constant pool" first. If the string already exists in the pool, a reference to the pooled instance is returned. If the string doesn't exist in the pool, a new string instance is created and placed in the pool. For example: In the above example, only one object will be created. Firstly, JVM will not find any string object with the value "Welcome" in string constant pool that is why it will create a new object. After that it will find the string with the value "Welcome" in the pool, it will not create a new object but will return the reference to the same instance. Note: String objects are stored in a special memory area known as the "string constant pool".Why Java uses the concept of String literal?To make Java more memory efficient (because no new objects are created if it exists already in the string constant pool). 2) By new keywordIn such case, JVM will create a new string object in normal (non-pool) heap memory, and the literal "Welcome" will be placed in the string constant pool. The variable s will refer to the object in a heap (non-pool). Java String ExampleStringExample.java Test it NowOutput: The above code, converts a char array into a String object. And displays the String objects s1, s2, and s3 on console using println() method. Java String class methodsThe java.lang.String class provides many useful methods to perform operations on sequence of char values. Strings, which are widely used in Java programming, are a sequence of characters. In the Java programming language, strings are objects. The Java platform provides the char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
1 class to create and manipulate strings.Creating StringsThe most direct way to create a string is to write: String greeting = "Hello world!"; In this case, "Hello world!" is a string literal—a series of characters in your code that is enclosed in double quotes. Whenever it encounters a string literal in your code, the compiler creates a char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
1 object with its value—in this case, char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
3.As with any other object, you can create char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
1 objects by using the char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
5 keyword and a constructor. The char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
1 class has thirteen constructors that allow you to provide the initial value of the string using different sources, such as an array of characters:char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
The last line of this code snippet displays char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
7.Note: The char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
1 class is immutable, so that once it is created a char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
1 object cannot be changed. The char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
1 class has a number of methods, some of which will be discussed below, that appear to modify strings. Since strings are immutable, what these methods really do is create and return a new string that contains the result of the operation.String LengthMethods used to obtain information about an object are known as accessor methods. One accessor method that you can use with strings is the String palindrome = "Dot saw I was Tod"; int len = palindrome.length();1 method, which returns the number of characters contained in the string object. After the following two lines of code have been executed, String palindrome = "Dot saw I was Tod"; int len = palindrome.length();2 equals 17: String palindrome = "Dot saw I was Tod"; int len = palindrome.length(); A palindrome is a word or sentence that is symmetric—it is spelled the same forward and backward, ignoring case and punctuation. Here is a short and inefficient program to reverse a palindrome string. It invokes the char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
1 method String palindrome = "Dot saw I was Tod"; int len = palindrome.length();4, which returns the ith character in the string, counting from 0.
public class StringDemo {
public static void main(String[] args) {
String palindrome = "Dot saw I was Tod";
int len = palindrome.length();
char[] tempCharArray = new char[len];
char[] charArray = new char[len];
// put original string in an
// array of chars
for (int i = 0; i < len; i++) {
tempCharArray[i] =
palindrome.charAt(i);
}
// reverse array of chars
for (int j = 0; j < len; j++) {
charArray[j] =
tempCharArray[len - 1 - j];
}
String reversePalindrome =
new String(charArray);
System.out.println(reversePalindrome);
}
}
Running the program produces this output: To accomplish the string reversal, the program had to convert the string to an array of characters (first String palindrome = "Dot saw I was Tod"; int len = palindrome.length();5 loop), reverse the array into a second array (second String palindrome = "Dot saw I was Tod"; int len = palindrome.length();5 loop), and then convert back to a string. The char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
1 class includes a method, String palindrome = "Dot saw I was Tod"; int len = palindrome.length();8, to convert a string, or a portion of a string, into an array of characters so we could replace the first String palindrome = "Dot saw I was Tod"; int len = palindrome.length();5 loop in the program above with palindrome.getChars(0, len, tempCharArray, 0); Concatenating StringsThe char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
1 class includes a method for concatenating two strings:This returns a new string that is string1 with string2 added to it at the end. You can also use the
public class StringDemo {
public static void main(String[] args) {
String palindrome = "Dot saw I was Tod";
int len = palindrome.length();
char[] tempCharArray = new char[len];
char[] charArray = new char[len];
// put original string in an
// array of chars
for (int i = 0; i < len; i++) {
tempCharArray[i] =
palindrome.charAt(i);
}
// reverse array of chars
for (int j = 0; j < len; j++) {
charArray[j] =
tempCharArray[len - 1 - j];
}
String reversePalindrome =
new String(charArray);
System.out.println(reversePalindrome);
}
}
1 method with string literals, as in:"My name is ".concat("Rumplestiltskin");
Strings are more commonly concatenated with the
public class StringDemo {
public static void main(String[] args) {
String palindrome = "Dot saw I was Tod";
int len = palindrome.length();
char[] tempCharArray = new char[len];
char[] charArray = new char[len];
// put original string in an
// array of chars
for (int i = 0; i < len; i++) {
tempCharArray[i] =
palindrome.charAt(i);
}
// reverse array of chars
for (int j = 0; j < len; j++) {
charArray[j] =
tempCharArray[len - 1 - j];
}
String reversePalindrome =
new String(charArray);
System.out.println(reversePalindrome);
}
}
2 operator, as in"Hello," + " world" + "!" which results in The
public class StringDemo {
public static void main(String[] args) {
String palindrome = "Dot saw I was Tod";
int len = palindrome.length();
char[] tempCharArray = new char[len];
char[] charArray = new char[len];
// put original string in an
// array of chars
for (int i = 0; i < len; i++) {
tempCharArray[i] =
palindrome.charAt(i);
}
// reverse array of chars
for (int j = 0; j < len; j++) {
charArray[j] =
tempCharArray[len - 1 - j];
}
String reversePalindrome =
new String(charArray);
System.out.println(reversePalindrome);
}
}
2 operator is widely used in
public class StringDemo {
public static void main(String[] args) {
String palindrome = "Dot saw I was Tod";
int len = palindrome.length();
char[] tempCharArray = new char[len];
char[] charArray = new char[len];
// put original string in an
// array of chars
for (int i = 0; i < len; i++) {
tempCharArray[i] =
palindrome.charAt(i);
}
// reverse array of chars
for (int j = 0; j < len; j++) {
charArray[j] =
tempCharArray[len - 1 - j];
}
String reversePalindrome =
new String(charArray);
System.out.println(reversePalindrome);
}
}
4 statements. For example:String string1 = "saw I was ";
System.out.println("Dot " + string1 + "Tod");
which prints Such a concatenation can be a mixture of any objects. For each object that is not a char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
1, its
public class StringDemo {
public static void main(String[] args) {
String palindrome = "Dot saw I was Tod";
int len = palindrome.length();
char[] tempCharArray = new char[len];
char[] charArray = new char[len];
// put original string in an
// array of chars
for (int i = 0; i < len; i++) {
tempCharArray[i] =
palindrome.charAt(i);
}
// reverse array of chars
for (int j = 0; j < len; j++) {
charArray[j] =
tempCharArray[len - 1 - j];
}
String reversePalindrome =
new String(charArray);
System.out.println(reversePalindrome);
}
}
6 method is called to convert it to a char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
1.Note: The Java programming language does not permit literal strings to span lines in source files, so you must use the
public class StringDemo {
public static void main(String[] args) {
String palindrome = "Dot saw I was Tod";
int len = palindrome.length();
char[] tempCharArray = new char[len];
char[] charArray = new char[len];
// put original string in an
// array of chars
for (int i = 0; i < len; i++) {
tempCharArray[i] =
palindrome.charAt(i);
}
// reverse array of chars
for (int j = 0; j < len; j++) {
charArray[j] =
tempCharArray[len - 1 - j];
}
String reversePalindrome =
new String(charArray);
System.out.println(reversePalindrome);
}
}
2 concatenation operator at the end of each line in a multi-line string. For example:String quote =
"Now is the time for all good " +
"men to come to the aid of their country.";
Breaking strings between lines using the
public class StringDemo {
public static void main(String[] args) {
String palindrome = "Dot saw I was Tod";
int len = palindrome.length();
char[] tempCharArray = new char[len];
char[] charArray = new char[len];
// put original string in an
// array of chars
for (int i = 0; i < len; i++) {
tempCharArray[i] =
palindrome.charAt(i);
}
// reverse array of chars
for (int j = 0; j < len; j++) {
charArray[j] =
tempCharArray[len - 1 - j];
}
String reversePalindrome =
new String(charArray);
System.out.println(reversePalindrome);
}
}
2 concatenation operator is, once again, very common in
public class StringDemo {
public static void main(String[] args) {
String palindrome = "Dot saw I was Tod";
int len = palindrome.length();
char[] tempCharArray = new char[len];
char[] charArray = new char[len];
// put original string in an
// array of chars
for (int i = 0; i < len; i++) {
tempCharArray[i] =
palindrome.charAt(i);
}
// reverse array of chars
for (int j = 0; j < len; j++) {
charArray[j] =
tempCharArray[len - 1 - j];
}
String reversePalindrome =
new String(charArray);
System.out.println(reversePalindrome);
}
}
4 statements.Creating Format StringsYou have seen the use of the palindrome.getChars(0, len, tempCharArray, 0);1 and palindrome.getChars(0, len, tempCharArray, 0);2 methods to print output with formatted numbers. The char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
1 class has an equivalent class method, palindrome.getChars(0, len, tempCharArray, 0);2, that returns a char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
String helloString = new String(helloArray);
System.out.println(helloString);
1 object rather than a palindrome.getChars(0, len, tempCharArray, 0);6 object. Using palindrome.getChars(0, len, tempCharArray, 0);7 static palindrome.getChars(0, len, tempCharArray, 0);2 method allows you to create a formatted string that you can reuse, as opposed to a one-time print statement. For example, instead of What is string s new string ()?For example: String s=new String(“Welcome”); It creates two objects (in String pool and in heap) and one reference variable where the variable 's' will refer to the object in the heap.
What is S in Java string?In Java, string is basically an object that represents sequence of char values. An array of characters works same as Java string. For example: char[] ch={'j','a','v','a','t','p','o','i','n','t'};
How many objects will be created string s new string Hello?The answer is: 2 String objects are created.
What will be the output of the following code string's new string ();?String s = new String(); This creates a new object of class String, and assigns it to the reference variable s.
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