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content/ta/fall2017/cpsc220/oct18.md

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+# October 18th
+
+## ArrayLists in classes
+
+```java
+public class Numbers {
+  private ArrayList<Integer> used;
+  private ArrayList<Integer> unused;
+  numbers () {
+    // Debug: System.out.println("1. Constructor Entry Point");
+    used = new ArrayList<Integer>();
+    unused = new ArrayList<Integer>();
+    // Debug: System.out.println("2, Constructor Size of ArrayLists" + used.size() + " " + unused.size())
+  }
+  // Adds the numbers 1-5 into the used ArrayList
+  public void fillUsedArrayList() {
+    for (int i = 0; i < 5; i++) {
+        used.add(i + 1);
+    }
+  }
+  // Move an item from the unused ArrayList to the used ArrayList
+  public int moveIt(int index) {
+    int temp = used.get(index);
+    unused.add(temp);
+    // Debug: System.out.println("Adding to used array:" + (i + 1));
+    used.remove(index);
+    return temp;
+  }
+  // The method below is created for debugging purposes
+  public void printBothArrayLists() {
+    // Print the used arraylist
+    System.out.println("Used ArrayList");
+    for (int i = 0; i < used.size(); i++) {
+        System.out.println(used.get(i));
+    }
+    
+    // Print the unused arraylist
+    System.out.println("Unused ArrayList");
+    for (int i = 0; i < unused.size(); i ++) {
+        System.out.println(unused.get(i));
+    }
+  }
+}
+```
+
+Recall that you can compile the code above but you cannot run it. To run code, you must have a main method.
+
+## NumberTester
+
+```java
+public class NumberTester {
+    public static void main(String[] args) {
+      Numbers list;
+      list = new Numbers();
+      list.fillUsedArrayList();
+      list.printBothArrayLists();
+    }
+}
+```
+
+
+
+
+
+## Difference between Array and ArrayList
+
+An Array is a **static** structure of contiguous memory of a single type.
+
+An ArrayList is a **dynamic** structure of contiguous memory of a single type	
+
+
+
+To get the size of an array you use `.length`
+
+To get the size of an ArrayList you use `.size()`