Arrays of Objects in AP CSA

An array of objects stores references, not the objects themselves. Each element must be individually constructed with new, and calling methods on an uninitialized element causes a NullPointerException.

Declaring and Populating

// Creates an array of 3 Student references -- all null!
Student[] roster = new Student[3];

// Each element must be separately constructed
roster[0] = new Student("Ana", 11);
roster[1] = new Student("Ben", 10);
roster[2] = new Student("Cara", 12);

Calling Methods on Array Elements

for (int i = 0; i < roster.length; i++) {
    System.out.println(roster[i].getName());  // calls method on each Student
    System.out.println(roster[i].getGrade());
}

Book[] shelf = new Book[3];
System.out.println(shelf[0].getTitle());