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content/ta/fall2017/cpsc220/oct4.md

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+# Lecture on October 4th
+
+## Pass by Copy vs Pass by Reference
+
+### Pass by Copy
+
+When you pass a primitive type into a method (int, char, double, float, etc), it makes a copy of the value of the variable and brings it into the method
+
+### Pass by Reference
+
+When you pass an array into a method (int[], char[], double[], etc[]), it passes in the reference of the variable into the method. In other words, you give the actual array into the method and allows the method to change it.
+
+### What's the Implication?
+
+If you change the primitive in a method, it doesn't actually change the value of the variable.
+
+If you pass in an array and change it in the method, it has been permanently changed outside the method as well.
+
+### How do I make it so I can't change my array by accident?
+
+Use the `final`keyword in the method header
+
+```java
+public static void printAll(final int[] array) {
+    for (int i = 0; i < array.length; i++) {
+        System.out.println("Number " + (i + 1) + " is " + array[i])
+    }
+}
+```
+