Overview of Strings

• Strings (java.lang.String) are pieces of text stored in Java programs.
• They are not primitive data types but are commonly used in Java programs.
• In Java, Strings are immutable, meaning they cannot be changed.

Section 1: Comparing Strings

Immutability of Strings

• Strings in Java are immutable, preventing any modification.

String Equality Comparison

• To compare Strings for equality, use the equals or equalsIgnoreCase methods.

  • Example:

    String firstString = "Test123";
    String secondString = "Test" + 123;
    
    if (firstString.equals(secondString)) {
       // Both Strings have the same content.
    }
    
    

  • Example (ignoring case):

    if (firstString.equalsIgnoreCase(secondString)) {
       // Both Strings are equal, ignoring the case of the individual characters.
    }
    
    

Locale Consideration

• equalsIgnoreCase doesn't let you specify a Locale, which might affect equality, e.g., in Turkish.
• Use toLowerCase(Locale) or toUpperCase(Locale) with equals for locale-sensitive comparisons.

  • Example:

    Locale locale = Locale.forLanguageTag("tr-TR");
    System.out.println(firstString.toLowerCase(locale).equals(secondString.toLowerCase(locale)));
    
    

Avoid Using == for String Comparison

• Do not use the == or != operators to compare Strings unless you can guarantee string internment.
• Use String.equals(Object) method for accurate value-based comparison.

Comparing Strings in a Switch Statement

• Starting from Java SE 7, you can compare a String variable to literals in a switch statement.
• Ensure the String is not null to avoid a NullPointerException.
• Values are compared using String.equals and are case-sensitive.

  • Example:

    String stringToSwitch = "A";
    switch (stringToSwitch) {
       case "a":
          System.out.println("a");
          break;
       case "A":
          System.out.println("A");
          break;
       case "B":
          System.out.println("B");
          break;
       default:
          break;
    }
    
    

Comparing Strings with Constant Values