Unit 7 Array Lists Collegeboard

• a reference type
  • mutatble and contains
• For loops
• While loops
• Enhanced for loops
  • for each loops
• using arrary lists with doubles
• Searching
  • the locating of data w/ linear structures
  • ie: arrays, lists, que, stack
  • involves control structures
• Sorting
  • ascending and descending order

vocab

• ArrayLists are similar to arrays, except that they are a mutable list of object references, meaning that the size of the list can be adjusted freely

import java.util.ArrayList;
public class ArrayListInit
{
    public static void main(String[] args)
    {
        //ArrayLists can only be initialized with Object data types.
        // This will cause an error because we are attempting to create an ArrayList with primitive type int.
        ArrayList<int> array = new ArrayList<int>();
        
        //Comment out the code above, and uncomment the code below to create a working ArrayList!
        // ArrayList<Integer> array = new ArrayList<Integer>();
        
        //We can also create an ArrayList without specifying the type
        //This is NOT RECOMMENDED because any errors made to the type will NOT be
        //discovered until after runtime.
        ArrayList arrayWithoutAType = new ArrayList();
        System.out.println("Congrats! You created an ArrayList!");
    }
}

//descending order and swapping first and last 
import java.util.ArrayList;
import java.util.Collections;

// Initializing an ArrayList filled with integers
ArrayList<Integer> integers = new ArrayList<>(Arrays.asList(37,64,92,84,1));

Collections.sort(integers);
Collections.reverse(integers);


System.out.println("Reverse order: " + integers);

public static void swap(){
    Integer temp = numbers.get(0);
    int last_index = integers.size()-1; 
    integers.set(0, integers.get(last_index));
    integers.set(last_index, temp);
    System.out.println("swapped the first and last numbers " + integers);
}

swap()

Reverse order: [92, 84, 64, 37, 1]
swapped the first and last numbers [1, 84, 64, 37, 92]

//hashcode 
import java.util.ArrayList;
import java.util.Collections;

// Initializing an ArrayList filled with integers
ArrayList<Integer> integers = new ArrayList<>(Arrays.asList(37,64,92,84,1));

Collections.sort(integers);

System.out.println("hash code: " + integers.hashCode());

hash code: 30719139