With objects, such as Strings, we can’t use the primitive equality operator == to check for equality between two strings. To test equality with strings, we use a built-in method called equals().

For example:

String flavor1 = "Mango";
String flavor2 = "Peach";

System.out.println(flavor1.equals("Mango"));
// prints true

System.out.println(flavor2.equals("Mango"));
// prints false

Side note, there’s also an equalsIgnoreCase() method that compares two strings without considering upper/lower cases.

Keep Reading: AP Computer Science A Students

We can also compare String values lexicographically (think dictionary order) using the .compareTo() method. When we call the .compareTo() method, each character is in the String is converted to Unicode; then the Unicode character from each String is compared.

The method will return an int that represents the difference between the two Strings.

For example:

String flavor1 = "Mango";
String flavor2 = "Peach";

System.out.println(flavor1.compareTo(flavor2)); 

Our program above will output -3.

When we use .compareTo(), we must pay attention to the return value:

• If the method returns 0, the two Strings are equal.
• If the value is less than 0, then the String object is lexicographically less than the String object argument.
• If the value is greater than 0, then the String object is lexicographically greater than the String object argument.

In the example above, "Mango" comes before "Peach", so we get a negative number (we specifically get -3 because the Unicode values of "M" and "P" differ by 3). If we did flavor2.compareTo(flavor1), we would get 3, signifying that "Peach" is greater than "Mango".

Note: Make sure to pay attention to capitalization when using .compareTo(). Upper case and lower case letters have different Unicode values. For example, when comparing "Mango" and "Peach", we got -3, meaning that "Mango" was smaller. But if we compare "mango" and "Peach" we get 29. The Unicode value for lower case "m" is actually larger than upper case "P". Using .compareToIgnoreCase() will perform the same task, but will not consider upper/lower case.