Introductions
- A reference type
- Array cannot be modified while ArrayLists can change size dynamically
Methods
- add(int index, element) ...
Traversing ArrayLists
- For Loop
- While Loop
- Enhanced ForLoop
Searching
- The locating of data within linear structures
- Searching a structure involves control structures - iterationnal and selection - loop with an if statement
- For loops are optimal for linear searching because each element needs to be specified sequentiallly with no need to track the index after its executed
- Order matters sometimes in searching
Sorting
- Sorting sorts the ArrayList in a specified order (ascending or descending)
- Collections.sort[(list.name)] - sort in ascending order
- Collections.sort[(ArrayList,Collections.reverseOrder())] - sort in ascending order
HW
Create an ArrayList that includes 2 of the 4 factors listed below.
- Sort an ArrayList in descending order and swap the first and last elements
- Find and display the hashCode of an Arraylist before and after being sorted
- Return "ascending" if the list is sorted in ascending order, return "descending" if it is descending, and return "neither" if neither
- Replace 3 elements in an ArrayList with another ArrayList and reverse the order of the new list
import java.util.ArrayList;
import java.util.Collections;
// initialize Array List with strings
ArrayList<String> strlist = new ArrayList<>();
strlist.add("apple");
strlist.add("orange");
strlist.add("3");
strlist.add("yellow");
strlist.add("AX7");
strlist.add("blue98");
System.out.println(strlist);
// reverse order of array list
Collections.reverse(strlist);
// switch first and last
public static void swap(){
String temp = strlist.get(0);
int lastindex = strlist.size()-1;
strlist.set(0, strlist.get(lastindex));
strlist.set(lastindex, temp);
System.out.println("reversed list with first and last element switched: " + strlist);
}
swap()
import java.util.ArrayList;
import java.util.Collections;
// initialize Array List with strings
ArrayList<String> strlist = new ArrayList<>();
strlist.add("apple");
strlist.add("orange");
strlist.add("3");
strlist.add("yellow");
strlist.add("AX7");
strlist.add("blue98");
// hashCode before sort
System.out.println("Unsorted hashCode: " + strlist.hashCode());
// hashCode after sort
Collections.sort(strlist);
System.out.println("Sorted hashCode: " + strlist.hashCode());