String Objects: Concatenation, Literals, and More

String Objects: Concatenation, Literals, and More

Understanding String Objects

  • A String object represents a sequence of characters and is an example of an object in object-oriented programming.
  • In Java, unlike other simple data types, Strings are objects created from the String class.
  • Strings can be created either by using the new keyword: String str = new String("Hello"); or by directly assigning a String literal to the String instance: String str = "Hello";.

String Literals

  • String literals are any text enclosed in double quotes, such as “Hello, World!”.
  • String literals are treated as instances of the String class in Java.
  • All string literals are automatically instances of the String class, there’s no need to explicitly create a new instance.
  • String literals in Java are immutable, meaning that once they’re created, they cannot be changed.

String Concatenation

  • String concatenation is the operation of joining two strings end-to-end.
  • In Java, string concatenation can be done using the + operator: e.g. String str = "Hello" + " World";.
  • If any of the operands of the + operator is a String, the operator acts as a concatenation operator and not an addition operator. For example: "Hello " + 123 produces the string "Hello 123".
  • The concat method in the String class can also be used to concatenate strings: e.g. String str = "Hello".concat(" World");.

Manipulating Strings

  • The String class in Java provides a lot of methods to work with strings, such as to obtain their length (length()), convert to upper or lower case (toUpperCase(), toLowerCase()), or replace characters (replace()).
  • Methods like substring(), charAt(), and split() etc., can be used to retrieve or manipulate parts of the String object.

Using == Operator and equals() Method

  • To compare the content of two String objects, the equals() or equalsIgnoreCase() methods should be used, not the == operator.
  • The == operator compares the references, not the content. So, == will only return true if two references are pointing to the same objects.
  • The equals() method compares whether the content is identical, even when the instances are different. For example: str1.equals(str2) will return true if str1 and str2 have the same characters in the same order.

Importance of String class

  • The class String is one of the most used classes in Java.
  • It provides a comprehensive set of operations that can be performed on Strings.
  • Mastering the use of String objects and their methods is fundamental to effective programming in Java.