描述

Discussion 2: Scope, Pass-byValue, Static Christine Zhou Agenda Announcements Worksheet #1 Worksheet #2 Worksheet #3 (if we can!) Administrivia Lab 1 and Lab 2 due this Friday 2/1 at midnight. ○ Note, all labs are due Friday at midnight the week they are assigned. Proj0 NBody also due Friday at midnight. ○ If you haven’t started please start ASAP! Office hours and exam prep/LOST sections start this week! See calendars on the course website. Pre-semester Advising: @414 or email me! Discussion survey: http://tinyurl.com/cz-disc2-sp19 ○ Good for me to collect your emails (in case I have announcements or mess up during discussion 😅) Review: Defining classes // class definition public class IntList { // instance variables int head; IntList tail; // constructors, which will create IntList objects public IntList() {...} public IntList(int value, IntList tail) {...} // you can create methods that use the instance variables! public void insert(int val) {...} public void removeLast() {...} } Review: Java’s Types Primitives: References: byte, short, long, int, double, float, char, boolean Everything else! Objects, arrays, Strings, etc. Review: Box and Pointer Diagrams Box and Pointers are the 61B equivalent of 61A’s environment diagram They are crucial to helping us keep track of what goes on in a program: use them! int x = 29; int x 29 Primitives go in the box int[] arr = new int[3]; We didn’t specify what integers are going in the array, so Java initializes it with the default value 0 int[ ] arr 0 0 0 Reference types are referenced via pointers Java is pass by value Golden Rule of Equals AKA pass-by-value When you do “a = b”, you always copy the bits (whatever is inside the box) of b into a. For primitives: Directly copy the value inside b to a. For Reference types: Copy the memory address of b into a. ○ Also can say “copies the pointer in b to a” int[ ] arr1 int x = 29; int y = x; int x int y 29 29 int[] arr1 = new int

AI 摘要