Computer Science A

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Week 19 FRQ - Array

FRQ - Array

1 min read
  • Arraylist
  • Warmup
  • Checklist to Maximize Points ✅
  • Common Mistakes to Avoid ❌

    • Array

    • fixed sized
    • single or multidimensional

    arrays

    1. Declare

    int[] arr1;
int[] arr2;

    2. Initialize

    //separating declare and initialize
arr1 = new int[5];
arr2 = new int[]{1,2,3};

// declare and initialize at the same time
int[] arr1 = new int[5];
int[] arr2 = {1,2,3}; // an array literal

    3. Access element using []

    arr2[0] // accesses the first element in the array

    Arraylist

    • resizable
    • uses methods to access and modify elements
    • typically stores objects

    How to Create Arraylists:

    1. Declare and Initialize
    ArrayList<String> al = new ArrayList<String>();
    1. Basic Operations

    Insertion using add()

    al.add("apple");
al.add("orange");
al.add("banana");

    Access using get()

    al.get(0);

    Deletion using remove()

    al.remove("orange");

    Update using set()

    al.set(0, "kiwi");

    Warmup

    Write a java program to sort an Arraylist

    Checklist to Maximize Points ✅

    Before Writing Code

    • Understand the method signature (what the methods do, the return types, access modifier)
    • Paying attention to input type (e.g. array vs ArrayList)

    Writing Code

    • Use loops carefully (consider bounds)
    • Check for null/empty cases

    Before Submitting Code

    • Correct return type
    • Check whether syntax is used for array/ArrayList

    Common Mistakes to Avoid ❌

    [] vs get Confusion (penalty)

    []: used to access elements in array

    get: used to access elements in ArrayList

    int[] arr = {1,2,3};
System.out.println(arr[0]); 

ArrayList<String> al = new ArrayList<String>();
al.add("sprite");
System.out.println(al.get(0));

    .length vs .size() Confusion (no penalty)

    .length: property for length of a array .size(): method for length of an Arraylist

    String[] colors;
colors = new String[]{"yellow", "purple", "blue"};
System.out.println(colors.length);

ArrayList<Integer> nums = new ArrayList<Integer>();
nums.add(12);
nums.add(10); 
System.out.println(nums.size());

    Traversing Arrays/ArrayLists

    • Ensure bounds are correct (applying the right comparison/logic)
    • Account for dynamic resizing of ArrayLists for .add() and .remove()
    // starts at the last index (.size() - 1)
// ends at the first index
for (int i = temps.size() - 1; temps >= 0; i--) {
    // insert code
}

    Scoring Criteria 📝

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