CS 231 Data Structures and Algorithms Fall 2018

Transcription

1 CS 231 Data Structures and Algorithms Fall 2018 Interface, Node Based Stack, Exception Handling, Class BufferedReader Lecture 12 October 1, 2018 Prof. Zadia Codabux 1

2 Agenda Node based implementation of stack Project 4 Tips Good vs. Bad Code Exception Handling BufferedReader Class Break and Continue split() Method 2

3 Administrative Homework will be uploaded this afternoon 3

4 Node-Based Stack Implementation public class NodeStack { private class Node {... // end of Node // end of NodeStack Demo: Node-based stack using generics (NodeStack.java) 4

5 Project 4 Tips 5

6 Bad.java import java.util.arraylist; public class Bad { ArrayList<Integer> list1 = new ArrayList<>(); ArrayList<Boolean> list2 = new ArrayList<>(); ArrayList<String> list3 = new ArrayList<>(); int myint = 52; // This is my method. I tell you essentially nothing about what it does and definitely don't help // the reader with defining what parameters are! public static void main(string[] args) { int i = 0; int j = 10; // Im not going to tell anyone what my complex thought process is :) if(i>j&&i<5&&j<0 i>10) System.out.println("Yikes!"); // Only I can run my code on my computer! String filepath = "/Users/myfolder/CS231/ProjectBlah/Blah/resource.pn g"; 6

7 Good.java /** * Name * class * Brief description * project */ import java.util.arraylist; public class Good { private ArrayList<Integer> list1; // Description above or here what field means if non-obvious private ArrayList<Boolean> list2; private ArrayList<String> list3; private int myint; /** * Default constructor. Instantiates all my fields. * * Parameters: * None */ public Good() { list1 = new ArrayList<>(); list2 = new ArrayList<>(); list3 = new ArrayList<>(); myint = 52; /** * main method: run my main code that clarifies how conditional blocks should be written and clauses * be indented. * * Parameters: * args: Arguments the user passes in as a String array to the command line. */ public static void main(string[] args) { int i = 0; int j = 10; // I use inline comments to clarify anything in my code that is non-obvious :) if (i > j && i < 5 && j < 0 i > 10) System.out.println("Much better!"); // Only anyone with my Project code folder can run my code! String filepath = "Blah/resource.png"; 7

8 Exception Handling Exceptions are a built-in class that is used for exiting methods when an error occurs. If an error occurs in a method so that it can't continue, it can "throw" an exception to the method that called it. Think of it as the second method throwing back to the caller the excuse for why it can't do what was expected of it. 8

9 Exception Handling Source: Google Image 9

10 Exception Handling That is the classical approach to handle an exception in Java. a try block that encloses the code section which might throw an exception, one or more catch blocks that handle the exception and a finally block which gets executed after the try block was successfully executed or a thrown exception was handled. The try block is required, and you can either catch or finally block. 10

11 Exception Handling try { //code that might raise an exception catch (ExceptionType1 ex1) { // exception handler for ExceptionType1 catch (ExceptionType2 ex2) { // exception handler for ExceptionType2 finally { // block of code to be executed after try block ends 11

12 Class BufferedReader BufferedReader is Java class to reads the text from an input stream (like a file) by buffering characters that seamlessly reads characters, arrays or lines Some common methods are: int read() - Reads a single character. String readline() - Reads a line of text. Example ReadFileEx.java void close() - Closes the stream and releases any system resources associated with it. Reference: 12

13 Break Break is used to exit or force termination of a loop and skip any remaining code of the loop body class BreakDemo { public static void main(string args[]) { System.out.println("break demo"); for (int i = 0; i < 10; i++) { //terminate loop when i is 5 if (i == 5) break; System.out.println("i: " + i); BreakDemo.java 13

14 Continue Continue causes the loop to immediately jump to the next iteration of the loop. class ContinueDemo { public static void main(string args[]) { System.out.println( continue demo"); for (int i = 0; i < 10; i++) { //When i is 5, skip and continue if (i == 5) continue; System.out.println("i: " + i); ContinueDemo.java 14

15 split() Method The method split() is used for splitting a String into its substrings based on the given delimiter/regular expression public class SplitDemo { public static void main(string[] args) { String str = "This is a split demo code"; for (String words: str.split(" ")) { System.out.println(words); SplitDemo.java 15