Arraylist Unit 7
Unit 7 Lesson
- Initializing an ArrayList
- Adding to an ArrayList
- Removing from an ArrayList
- Getting the size of an ArrayList
- Sorting
- Searching
- Homework Hacks
Initializing an ArrayList
ArrayList<Type> someName = new ArrayList<Type>();
Adding to an ArrayList
someName.add(someValue);
Removing from an ArrayList
someName.remove(someValue);
Getting the size of an ArrayList
someName.size();
Sorting
Collections.sort(someName);Collections.sort(someName, Collections.naturalOrder());
Searching
- Can use iteration and selection to search
- For loop, for each loop, while loop
Homework Hacks
- 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.*;
public class ArraylistHacks {
public ArrayList<Integer> initial_list;
public ArrayList<Integer> sortswapped_list;
public String ascdesc = "Neither";
public ArraylistHacks(ArrayList<Integer> x) {
// Clone arraylist to avoid overriding values of initial
this.initial_list = (ArrayList<Integer>) x.clone();
this.sortswapped_list = (ArrayList<Integer>) x.clone();
ascDescTest();
sortAndSwap();
}
public void sortAndSwap() {
// sorting the arraylist
Collections.sort(sortswapped_list);
Collections.swap(sortswapped_list, 0, sortswapped_list.size() - 1);
}
public void ascDescTest() {
boolean asc = true;
boolean desc = true;
for (int i = 0; i < initial_list.size() - 1; i++) {
// Test if ascending
if (!(initial_list.get(i) <= initial_list.get(i + 1))) {
asc = false;
}
// Test if descending
if (!(initial_list.get(i) >= initial_list.get(i + 1))) {
desc = false;
}
}
// if asc or desc booleans are true, change string output
if (asc) {
this.ascdesc = "Ascending";
}
else if (desc) {
this.ascdesc = "Descending";
}
}
public void hacksToString() {
System.out.println("-----");
System.out.println("Initial: " + this.initial_list);
System.out.println("Ascending/Descending: " + this.ascdesc);
System.out.println("Sort + Swap: " + this.sortswapped_list);
}
}
ArrayList<Integer> alist = new ArrayList<Integer>();
alist.add(3);
alist.add(2);
alist.add(5);
alist.add(7);
alist.add(12);
ArrayList<Integer> blist = new ArrayList<Integer>();
blist.add(1);
blist.add(2);
blist.add(4);
blist.add(6);
blist.add(8);
ArrayList<Integer> clist = new ArrayList<Integer>();
clist.add(9);
clist.add(8);
clist.add(7);
clist.add(6);
clist.add(5);
ArraylistHacks a = new ArraylistHacks(alist);
a.hacksToString();
ArraylistHacks b = new ArraylistHacks(blist);
b.hacksToString();
ArraylistHacks c = new ArraylistHacks(clist);
c.hacksToString();