[讨论]UC Berkeley EECS 61B: Data Structures & Algorithms in Java

小K 发表于 2014-1-13 09:55
61B midterm 只看见答案没看见题目，这个哪里有？

我觉得midterm或者final题目都不会放出来吧。
我看过的公共课或者校内课的网页都没有。
可能是每年的题目有重复？
我们学校也是大力封锁各种试题的

rsun 发表于 2014-1-12 21:03
我觉得midterm或者final题目都不会放出来吧。
我看过的公共课或者校内课的网页都没有。
可能是每年的题 ...

哦好吧。。。本来还想考察一下自己学的如何的 :(

对了，学完61b还想继续用java做具体的事情，而不是另外学一门语言的话，怎么比较好呢？
继续上课，还是开始刷题目，or others?

小K 发表于 2014-1-13 10:05
哦好吧。。。本来还想考察一下自己学的如何的 :(

偶然看到课程介绍里有这么一句话，貌似试卷网上没有但是可以在berkeley的书店买到？
如果是在国内，能买到的书，，几乎是必然有电子版啊
You should also buy the class reader, available at Vick Copy at 1879 Euclid, near Hearst. The bulk of the reader is old CS 61B exams, which will not be provided online (though the solutions are). By far the best way to study for the exams is to try the old ones. The remainder of the reader is information on using the compiler, debugger, and editor.

求讨论，我不确定我答案是对的

http://www.cs.berkeley.edu/~jrs/61b/lab/lab5/readme

  ((Superclass) subclassvariable).method();
我以为可以调用Super class的方法，但是居然不是的。。。为啥？
some code here, 求能人给看看啊啊啊
这个例子里面，没有什么办法能把Array of a superClass cast 成为 Array of subClass，我漏掉了什么吗？

1. 
   
2. 
   
3. // Part I:  Assignments and Casting (1 point)
   
4. // ------------------------------------------
   
5. // Let Y be a subclass of X, and let y and x be variables of classes Y and X
   
6. // respectively.  From lecture, you know that the assignment "x = y" is valid, but
   
7. // the assignment "y = (Y) x" requires a cast to compile, and will cause a
   
8. // run-time error if x references an object that isn't a Y.
   
9. 
   
10. // What about arrays of objects?  Suppose xa is an array of X's, and ya is an
    
11. // array of Y's.
    
12. 
    
13. 
    
14. 
    
15. 
    
16. class X{  //Animal
    
17.         protected int a = 1;
    
18.         public int aa(){return (1);}
    
19. }
    
20. 
    
21. class Y extends X{ //Dog
    
22.         protected int a = 2;
    
23.         public int aa(){return(2);}
    
24. }
    
25. 
    
26. class Z extends X{ //Cat
    
27.         protected int a = 3;
    
28.         public int aa(){return(3);}
    
29. }
    
30. 
    
31. class testClass{
    
32.         public static void main(String[] args){
    
33.                 X x = new X();
    
34.                 Y y = new Y();
    
35. 
    
36.                 x = y;
    
37.                 y = (Y) x;
    
38. 
    
39.                 X[] xa = new X[5];
    
40.                 Y[] ya = new Y[3];
    
41. 
    
42. // (a)  At compile-time, can we assign xa to ya, and vice versa?  When is a cast
    
43. //      required?
    
44. // can assign Dog to Animal, but not vice versa, without casting
    
45.                 xa = ya;
    
46. 
    
47.                 X[] xa2 = new X[2];
    
48.                 Y[] ya2 = new Y[3];
    
49. 
    
50. // (b)  At run-time, if ya references an array of Y's, can we assign it to xa?
    
51. //      Can we then assign it back from xa to ya?
    
52.                 // Yes can assign Array of Dogs to Animals,  then assign back is also ok
    
53.                 // ya2 = (Y[]) xa2; // can compile, run time error, can't assign animals as dogs.
    
54.                 xa2[0] = new Y();
    
55.                 xa2[1] = new Y();
    
56.                 // ya2 = (Y[]) xa2; // still doesn't work, same run time error
    
57.                 xa2 = ya2;
    
58. 
    
59.                 X[] za = new X[2]; // array of animals
    
60.                 // za[0] = new Z(); // this can be non assigned
    
61.                 za[1] = new Z();
    
62. // (c)  If xa references an array of X's (that are not Y's), can we assign it to
    
63. //      ya?  Can we then assign it back from ya to xa?  Does it make a difference
    
64. //      if the array of type X[] references objects that are all of class Y?  Why
    
65. //      do you think this is the case?
    
66. 
    
67. 
    
68.                 // ya = (y[]) za; // run time error!! can not cast cats to dogs
    
69. 
    
70.                 za = new X[2];
    
71.                 za[0]=new Y();
    
72.                 za[1]=new Y();
    
73. 
    
74.                 // ya = (Y[]) za;// run time error!! can not cast cats to dogs
    
75.         }
    
76. }
    

复制代码

(b)  Define a variable whose static type is the superclass and which references
     an object of the superclass (but not the subclass).  If we cast the
     variable to the subclass type before calling the method, does Java call
     the superclass method or the subclass method?
可是这个不能cast啊。。。

from outside sub class, there is no way to access super class methods, without a special method of sub class written just to access super class methods. ------ is this right? 所以无论怎么cast， methods都只按本来的type而不是cast以后的type??

这么简单一个lab5还做了两小时我会承认吗。。。。。。但是终于弄明白了真好~~~

小K 发表于 2014-1-16 15:49
这么简单一个lab5还做了两小时我会承认吗。。。。。。但是终于弄明白了真好~~~

K姐
我现在也在跟这个课
我看到Lab1 里面写的 还要ta check off...还要注册什么账号
怎么感觉lab这种作业。。我们好像没有权限做似的

求解
lab能跟么？有其他入口？

求问这个课的作业是在Linux系统完成的吗？ 还是说windows上安装Java也可以？