compareTo() vs equals() in AP CSA

Two of the most commonly confused String methods on the AP exam. equals() answers a yes/no question. compareTo() answers a “who comes first?” question. Knowing which to use — and what they return — is tested every year.

equals() — True or False

equals() returns a boolean: true if the two Strings have identical characters, false otherwise. Case matters.

String a = "hello";
String b = "hello";
String c = "Hello";

System.out.println(a.equals(b));  // true
System.out.println(a.equals(c));  // false  (case-sensitive)
System.out.println(a == b);       // true in this case (string pool)
                                  // but NOT reliable -- never use ==

Use equalsIgnoreCase() when case should not matter:

System.out.println(a.equalsIgnoreCase(c));  // true

compareTo() — Returns an int

compareTo() returns an integer, not a boolean. The sign tells you the relationship:

String x = "apple";
String y = "banana";

int result = x.compareTo(y);
System.out.println(result);    // negative (apple comes before banana)

if (x.compareTo(y) < 0) {
    System.out.println(x + " comes first");
}

When to Use Which

String p = "Cat";
String q = "cat";
System.out.println(p.compareTo(q));