Learning Goals LG1: Implement the peer instruction process by A) clicking in on an answer B) discussing with your team C) coming to consensus and

Transcription

1 Learning Goals LG1: Implement the peer instruction process by A) clicking in on an answer B) discussing with your team C) coming to consensus and re-clicking in LG2: Describe the difference between the Dr. Java interaction pane and definition pane (using IM and as a metaphor). LG3: Describe how = is different in programming than it is in math. LG4: Be able to track a turtle s path by reading and tracing code LG5: Identify common errors in Java code and use computing terminology to describe them LG6: Read and modify a method to perform a given task with a Turtle. Specifically understand the use of a parameter to a method. LG7: Know which methods get stored in Turtle.java and which get stored in their own files (and why). LG8: Describe return values of methods and identify ones from methods you have used LG9: Nest several method calls in one statement (in contrast to doing multiple assignments) LG10: Explain how bits (0s and 1s) in a computer s memory can be interpreted in a variety of ways (depending on issues of type and representation) LG11: Use a for each loop in Java to loop over all pixels in a picture and perform a transformation on those pixels (e.g. decrease their red component). LG12: Apply Java syntax to cast a variable to another value (and explain how it s useful in setting picture colors). LG13: Read and understand a while loop for modifying a Picture. LG14: Describe the single array representation of pixels in Picture.java LG15: Be able to draw the CSE8A memory model for a program that uses a loop to modify a picture. LG16: Find bugs in code including: a common empty loop bug, using the how many times does this statement get executed analysis technique. LG17: Argue about the best location of a print statement to debug a problem with a loop. LG18: Trace the execution of a code through several method calls LG20: (LG 19 is missing) Read and trace execution of a code with a for loop (using a single array of pixels). LG21: Read and trace execution of a nested loop that loops over a Picture object LG22: Analyze given code to understand complex (requiring a mathematical expression) indexing into Pictures to mirror images by using the trace a few iterations technique. LG23: Compare and contrast a growth mindset and a fixed mindset as applied to programming. LG24: Read and code nested loops to perform mirroring (and related) transformations using nested loops. LG25: Employ the technique of drawing examples to explore various cases with 2-D array manipulation. LG26: Read, trace, and write code that performs a transformation over a restricted set of pixels (like a box of pixels). LG27: Read, trace and write a method that uses more than one Picture object (including where one Picture is the calling object). LG28: Apply Java scoping and simple parameter passing rules to draw a memory model that traces the execution of a method call. LG29: Read and trace loops which contain if statements.

2 Sample CSE8A midterm Length is not related to exam length Multiple Choice (circle one) 1. Evaluate the following expressions: Assume variables with the following names and values: int moos = 2; int quacks = 9; Expression 1: (quacks % 3) == moos) 1. The Boolean expression above evaluates to which? true false (quacks >=9) true false (quacks / moos) true false a. How many lines of output would be printed by the following code? for (int i = 0; i <= 40; i++) for (int j = 0; j < 3; j++) System.out.println("Ha!"); (a) 3 (b) 4 (c) 40 (d) 41 (e) 43 (f) 44 (g) 120 (h) 123 2b. Using the code above, trace the values of the iterators i and j for the first 7 iterations: i j

3 3. Choose all the statements that are true about the Java concept of scope. A) Scope is how you know how many parameters to use B) Scope is how you know what variable names can be referenced C) Scope is why variables in one program must have the same name as variables in another program. D) Scope is defined between an open curly brace and the NEXT closing curly brace. E) Scope is defined between an open curly brace and the matching closing curly brace. F) A variable can be referred to by name outside it s scope. 4. Give the method header of 3 methods that can be called on a Pixel object? Be sure to write the full method header. 5. Give the method header of 3 methods that can be called on a Turtle object? Be sure to write the full method header 6. Fix the following code so that it compiles and runs without runtime errors. There are at LEAST 3 errors to find (there may be more). Assume the code is in the file Picture.java You can write out the changes needed on the right hand side, referencing line numbers. 1. public void makeallwhite() index = 0; 4. pixelarray = getpixels(); 5. pixelobj = pixelarray[index]; 6. while (index <= pixelarray.length+1) pixelobj.setblue(255); 9. pixelobj.setgreen(255); 10. pixelobj.setred(255); 11. index++;

4 7. For the following for loop, write the code for an equivalent while loop. Assume this method is in Picture.java. public void foo() int c; Pixel[] b = this.getpixels(); for (int a = 0; a < b.length; a++) c = (int)b.getblue() *.2; b[a].setblue(c); 7b. In the above code, underline the part of the code where a Pixel object has its value modified. 8. What does this code do? Give a high level answer in complete English sentences. public void foo() Pixel[] b = this.getpixels(); for (int a = 0; a < b.length; a+= 3) b[a].setcolor(255,255,255);

5 9. What does this code do? Give a high level answer in complete English sentences. public void foo() Pixel b; for (int a = 0; a < this.getwidth(); a++) for (int c= 0; c < this.getheight(); c+=3) b = this.getpixel(a,c); b.setcolor(255,255,255); 10. We asked programmer Joe to write a method for Picture.java that would replace the left half of the calling object picture with the right half of another picture (passed in as a parameter). We promised Joe that the picture that would be provided as a parameter would be of the same size (height and width) as the calling object picture. Below is some code that Joe got started on, but he just went on vacation. Can you help out the customer and complete the program by filling in the missing lines? public void replaceleftwithright( ) for (int x = 0; x < this.getwidth()/2; x++) for (int y = 0; y < this.getheight(); y++) 11. Describe at least 3 differences between a growth mindset and a fixed mindset.

6 12. What is printed when the following code is executed by running the main method in Test12.java Code in Test12.java public static void main(string[] args) int foo = 3; int bar = 5; Color foobar = new Color(255,0,0); Picture p = new Picture( barbara1.jpg ); p.question12(foo,bar,foobar); Code in Picture.java public void question12(int bar, int foo, Color flubber) System.out.println(foo); System.out.println(bar); Color fb = new Color(0,0,255); System.out.println(flubber == fb);

7 13. Circle the best explanation for the use of the cast in the code below public void changepicture() Pixel[] foo = this.getpixels(); for (int i = 0; i < foo.length; i++) int newgreen = (int) (foo.getred()*.50 +foo.getblue()*.50); foo.setgreen(newgreen); A) The cast is needed since we are trying to use blue and red to make a green component. B) The cast is needed since we are adding two values to produce the green component. C) The cast is needed since we are multiplying a value by a non-integer number to produce the green component. D) The cast is needed since we are setting a color (green) component. E) The cast is needed since we are doing math (of any kind). 14. Write a method (assume it will be in Picture.java) to reduce the red, blue and green components by a particular amount (percentage). Assume the amount to reduce each component by is passed in as a parameter (there will be three parameters). The method should modify the calling object. (do on a separate page) 15. Write a method (assume it will be in Pictrue.java) to flip the pixels around a rectangle of height 25 and width 10. The center of the rectangle to be flipped will be passed as two parameters (width then height) to the method. You should flip around a horizontal line (from left to right). The method should modify the calling object. (do on a separate page)

8 16. Here you will write the code for a method (called bar in the file Picture.java). This method will return the largest number of blue pixels (blue greater than 200) in any given any row of the picture. (The search does not extend past the end of a row, so the max value is the width.) The following list of 16 statements is broken into 8 groups of 2 (i.e. 8 pairs). The correct definition of the bar() method can be formed using exactly ONE statement from each pair. The pairs themselves are given in a random order, so you will need to select the correct statement from each pair as well as determine the correct order for the statements. if (p.getblue() > 200) if (p.getcolor() > 200) for(int aaa = 0; aaa<this.getheight();aaa++) for(int aaa = 0; aaa<this.getheight()-1;aaa++) res = temp; temp = res; p = this.getpixel(bbb,aaa); p = this.getpixel(aaa,bbb); if(temp > res) if(temp < res) int temp = 0; int temp = 1; temp++; res++; for(int bbb = 0; bbb < this.getwidth();bbb++) for(int bbb = 0; bbb < this.getwidth()-1;bbb++) Select a statement from each pair and use it to fill in the method below: (be sure to add and use indenting appropriately)! public int bar() int res = 0; Pixel p = null; return res;