String Class in Java

Strings are integral component of any programming langage, representing sequences of Characters.The String Class in Java Provides a roboust set of methods and functionalities for working with textual data effeciently.

Contents hide

1 String Creation in Java

1.1 Using String Literals

1.2 Important Points Related to String Creation by Using String Literal in Java

1.3 Using new Keyword

2 Constructor of String Class

3 Important Methods for String

3.1 chatAt()

3.2 concat()

3.3 equals()

3.4 equalsIgnoreCase()

3.5 substring()

3.6 Java Substring Example

3.7 length()

3.8 replace()

3.9 trim()

4 Similar Java Tutorials

In String Class is a part of java.lang package and is automatically imported into every Java program. This means that you can strings without explicity importing the ‘String’ Class.

String Creation in Java

In Java we can create String in two ways either by using String litterals or by using new keyword.

Using String Literals

String str = "The Code Data";

In this case, only one Object is created in SCP (String Constant Pool), and “str” will always point to that Object.

Important Points Related to String Creation by Using String Literal in Java

Object Creation in String Constant Pool is Optional. first, it will check if any object already exists in the string constant pool with the same value. if the object already exists then the existing object will be reused. if an object does not exist, only a new object will be created. This condition only applies to the String constant pool, not the heap area.
The garbage collector is not allowed to access the String constant pool area.
All String pool constant objects will be destroyed automatically at the time of JVM shutdown.

Using new Keyword

String str = new String("The Code Data");

In this case, two Object is created one in the Heap Area and another in SCP (String Constant Pool), and “str” will always point to the Heap Object.

Note-

Whenever we are using a new operator compulsory a new object will be created in the Heap area. Hence there may be a chance of existing two or more objects with the same value in the Heap area but it is not possible in the String constant pool.

Constructor of String Class

String str = new String();

This constructor will create an empty String object.

String str = new String(String literals);

This constructor will create a String object for a given String literal.

String str = new String(StringBuffer strBuf);

This constructor will create an equivalent String object for a given StringBuffer.

String str = new String(char[] chArray);

This constructor will create an equivalent String object for a given char array.

String str = new String(byte[] byteArray);

This constructor will create an equivalent String object for a given byte array.

Important Methods for String

chatAt()

public char charAt(     @Range(from = 0, to = Integer.MAX_VALUE)  int index )

This method will return the character present at the given index.

concat()

public String concat(     @NotNull  String str )

This method concatenates the given String at the end of the current String.

equals()

public boolean equals( @Nullable  Object anObject )

This method is used to perform a String comparison where the case is important.

equalsIgnoreCase()

public boolean equalsIgnoreCase (@Nullable  String anotherString )

This method is used to perform a String comparison where the case is not important.

substring()

public String substring( @Range(from = 0, to = Integer.MAX_VALUE)  int beginIndex )

This method returns a substring from beginIndex to end of string.

public String substring(     @Range(from = 0, to = Integer.MAX_VALUE)  int beginIndex,
    @Range(from = 0, to = Integer.MAX_VALUE)  int endIndex )

This method return a substring from beginIndex to endIndex-1 index.

Java Substring Example

class StringMethod{
    public static void main(String[] args) {
        String s = "The Code Data";
        String subString1=  s.substring(4);
        String subString2=  s.substring(4,8);
        System.out.println(subString1);
        System.out.println(subString2);
    }
}

length()

public int length()

This method returns no of character present in the string.

Note- lenght is applicable for arrays but not for String Object while lenght() is applicable for String Object but not for arrays.

replace()

public String replace( char oldChar,
char newChar )

replace method returns a string after replacing oldChar by newChar.

trim()

public String trim()

This method is used to remove blank spaces present at the beginning and end of the string but not to remove blank spaces at the middle.

Note – Because of run time operation if there is a change in the value then with those changes a new object will be created in the Heap Memory. If there is no change in value then the existing object will be reused and no new object will be created whether the object is present in Heap Memory or String Constant Pool (SCP) the rule is samethe .