Java String class

Java String class

Strings are widely used in Java programming, where strings belong to objects, and Java provides String classes to create and manipulate strings.

Create a string

The easiest way to create a string is as follows:

String greeting = "Hello world!";

When you encounter a string constant in your code, the value here is "Hello world!" and the compiler uses that value to create a String object.

Like other objects, you can use keywords and construction methods to create String objects.

The String class has 11 construction methods that provide different parameters to initialize strings, such as an array of characters:

public class StringDemo{

   public static void main(String args[]){
      char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.'};
      String helloString = new String(helloArray);  
      System.out.println( helloString );
   }
}

The above examples compile and run as follows:

hello.

Note: T he String class is imm changed, so once you create a String object, its value cannot be changed. If you need to make a lot of changes to the string, you should choose to use the StringBuffer and StringBuilder classes.

The length of the string

The method used to get information about an object is called the accessor method.

One accessor method of the String class is the length() method, which returns the number of characters that the string object contains.

After the following code is executed, the len variable is equal to 17:

public class StringDemo {

   public static void main(String args[]) {
      String palindrome = "Dot saw I was Tod";
      int len = palindrome.length();
      System.out.println( "String Length is : " + len );
   }
}

The above examples compile and run as follows:

String Length is : 17

The connection string

The String class provides a way to connect two strings:

string1.concat(string2);

Returns a new string for string2 connection string1. You can also use the concat() method for string constants, such as:

"My name is ".concat("Zara");

It is more common to use the 'plus' operator to connect strings, such as:

"Hello," + " world" + "!"

The results are as follows:

"Hello, world!"

Here's an example:

public class StringDemo {
   public static void main(String args[]) {     
   String string1 = "saw I was ";     
   System.out.println("Dot " + string1 + "Tod");  
}
}

The above examples compile and run as follows:

Dot saw I was Tod

Create a formatted string

We know that output formatted numbers can use the printf() and format() methods. The String class uses the static method format() to return a String object instead of a PrintStream object.

The static method format() of the String class can be used to create reusable formatted strings, not just for one printout. Here's what it looks like:

System.out.printf("The value of the float variable is " +
                  "%f, while the value of the integer " +
                  "variable is %d, and the string " +
                  "is %s", floatVar, intVar, stringVar);

You can write like that, too

String fs;
fs = String.format("The value of the float variable is " +
                   "%f, while the value of the integer " +
                   "variable is %d, and the string " +
                   "is %s", floatVar, intVar, stringVar);
System.out.println(fs);

String method

Here's how the String class supports it, see the Java API documentation for more detail: