1. CompSci 230 S2 2015 Software Construction Introduction to Java

2. Today’s Agenda  Topics:  How does Java compare with Python?  Hello World in Java and Python  Setting Up and Getting Started in Java Programming  Notepad++, TextPad, Eclipse  Java Syntax  Reading:  The Java Tutorials  http://docs.oracle.com/javase/tutorial/ http://docs.oracle.com/javase/tutorial/  Welcome to Java for Python Programmers  http://interactivepython.org/courselib/static/java4python/index.html 012

3. How does Java compare with Python?  Java:  Python:  Java programs are “robust” if they are well-tested: reliable behaviour.  Python is not a strongly-typed language, so a method can produce strange results if given an unexpected input. More difficult to test, so less “robust”? SimpleArchitecture neutral Object orientedPortable DistributedHigh performance(?) MultithreadedRobust (as defined by Gosling)defined by Gosling DynamicSecure Simpler than JavaArchitecture neutral Object orientedPortable DistributedAdequate performance MultithreadedLess robust? More dynamic than JavaMore difficult to secure? 013

4. Python Vs Java  Python:  the syntax is sparse, and clear.  the underlying model of how objects and variables work is very consistent.  You can write powerful and interesting programs without a lot of work.  Java:  For very large programs Java and C++ are going to give you the best performance.  Maintainability is very important too. 014

5. Dynamic vs Static Typing  It is the way that each language handles variables.  Java forces you to define the type of a variable when you first declare it and will not allow you to change the type later in the program.  This is known as static typing.  Python uses dynamic typing, which allows you to change the type of a variable, by replacing an integer with a string.  Pros & Cons  Dynamic typing is easier for the novice programmer to get to grips with  without worrying too much about their types  However,  Static typing reduces the risk of undetected errors plaguing your program  It is easy to misspell a variable name and accidentally create a whole new variable 015

6. Braces vs Indentation  Python:  uses indentation to separate code into blocks  Java:  uses curly braces to define the beginning and end of each function and class definition 016

7. Speed vs Portability  Java:  It can be used to create platform-independent applications.  Any computer or mobile device that is able to run the Java virtual machine can run a Java application  Python:  You need a compiler that can turn Python code into code that your particular operating system can understand.  But, Java programs run more slowly than Python programs. 017

8. Python vs Java: Which is Easier to Use?  Most programmers agree that Python is an easier language for novice programmers to learn.  You will progress faster if you are learning Python as a first language than Java.  However, the popularity of Java means that learning this powerful language is essential if you want to develop apps for Android, for example. 018

9. Java: A Compiled and Interpreted Language  “In the Java programming language, all source code is first written in plain text files ending with the.java extension.  “Those source files are then compiled into.class files by the javac compiler.  “A.class file does not contain code that is native to your processor;  “it instead contains bytecodes — the machine language of the Java Virtual Machine (Java VM).  “The java launcher tool then runs your application [by interpreting its bytecode on] an instance of the Java Virtual Machine.”  Source: http://docs.oracle.com/javase/tutorial/getStarted/intro/definition.htmlhttp://docs.oracle.com/javase/tutorial/getStarted/intro/definition.html 019

10. Java – a mixed system  Java source code (MyProgram.java) Java byte code (MyProgram.class) javac.exe java.exe Computer 1Computer 2Computer 3 0110

11. Hello World program  Note: Python has a command-line interface which will execute a single line of code immediately after you type it  Python Source code: Hello.py  Print the Hello World! message  Java Source code: Hello.java  Print the Hello World! message public class Hello { public static void main(String[] args) { System.out.println("Hello world!"); } public class Hello { public static void main(String[] args) { System.out.println("Hello world!"); } def main(): print("Hello world!") main() def main(): print("Hello world!") main() Python Java Output 0111

12. Setting up your computer  Installing Java:  http://www.oracle.com/technetwork/java/javase/downloads/index.html  Choose Java SE Downloads -> Java Platform (JDK) 8u45  Click “Accept License Agreement”  Choose Platform and the version number (JDK 8 or jdk1.8.0_45)  There are several equivalent names  Java Standard Edition Development Kit  Java SE Development Kit  JDK  Usually Java is installed in the "Program Files" folder in the C drive of your computer.  Have you installed the JDK correctly?  Type “cmd” in the start menu  Enter “java -version“ in the command prompt window. It should print the version information. 0112

13. Setting up your computer  You can use any IDE (Example: Notepad++, Textpad, Eclipse, etc)  Please check our course website to get information regarding to setting up Notepad++ and textpad for Java programming  You can add commands to compile and run java programs  All Java files have the extension.java. Our programs will consist of TWO source files:  To compile Java programs we use the javac command,  To run an application we use the java command, e.g. javac MyProgram.java java MyApplication javac MyApplication.java contains the instructions describing what we want the program to do starts our program (a bit like a starter motor in a car) MyProgram.java MyApplication.java 0113

14. Java programs don't run.  You may have problem in your Path variable on your system.  Check the following  In the start menu, type “cmd”  Type “javac” + press ENTER key  It should display “Usage: javac… “  Otherwise, follow the steps below:  How to fix it:  Go to the C drive, open the Program Files folder, open the Java folder and open the jdk version folder (jdk1.8.x_x) and open the bin folder:  Check that java.exe and javac.exe are in this folder  Now copy the path to the JDK version you are running, e.g. C:\Program Files\Java\jdk1.8.0_45\bin 0114

15. Java programs don't run. (con’t)  Type “System” in the start menu and choose System from Control Panel  Click “Advanced system settings” on the left menu  Select the “Advanced” tab and click "Environment Variables“ button  Edit the Path System variable  Insert the path to your JDK after one of the first ";". Your path must be between two ";". …;SYSTEMROOT%\System32; C:\Program Files\Java\jdk1.8.0_45\bin 0115

16. Structure of a Java program  Important Rules:  Every Java program must define a class, all code is inside a class.  Everything in Java must have a type  Every Executable Java program must have a function called public static void main(String[] args)  And contains the statements (commands) to be executed. public class MyApplication { public static void main(String[] args) { MyProgram p = new MyProgram(); p.start(); } public class MyApplication { public static void main(String[] args) { MyProgram p = new MyProgram(); p.start(); } public class MyProgram { public void start() { System.out.println("Start!"); } public class MyProgram { public void start() { System.out.println("Start!"); } Class name Method name 0116

17. Structure of a Java program  public static void main(String[] args):  the following lines look similar but are in fact treated by Java as completely different methods  public void main(String[] args)  public static void main(String args)  public static void main()  void main(String args)  public indicates to the Java compiler that this is a method that anyone can call  static tells Java that this is a method that is part of the class, but is not a method for any one instance of the class  void tells the Java compiler that the method main will not return a value  args: It is a parameter list for the main method. It is an array of Strings 0117

18. Syntax  syntax: The set of legal structures and commands that can be used in a particular language.  Every basic Java statement ends with a semicolon ;  The contents of a class or method occur between { and }  syntax error (compiler error): A problem in the structure of a program that causes the compiler to fail.  Missing semicolon  Too many or too few { } braces  Illegal identifier for class name  Class and file names do not match ... 0118

19. Syntax error example 1 public class Hello { 2 pooblic static void main(String[] args) { 3 System.owt.println("Hello, world!")_ 4 } 5 }  Compiler output: Hello.java:2: expected pooblic static void main(String[] args) { ^ Hello.java:3: ';' expected } ^ 2 errors  The compiler shows the line number where it found the error.  The error messages can be tough to understand! 0119

20. Comments  Comments:  Ignored by the compiler  Aimed at people who read the code  Inline comments  All text until end of line is ignored e.g.  Multi-line comments  All text between start and end of comment is ignored e.g. // comment goes here /* comment goes in this space, here */ 0120

21. Data Types  Python:  Integers are objects, floating point numbers are objects, lists are objects, everything  Java:  Most basic data types like integers and floating point numbers are not objects. They are called primitive data types. Operations on the primitives are fast  There are eight primitive types :  Integers (whole numbers):  Floating-point numbers (decimal numbers):  Characters (symbol in character set (text)):  boolean (true or false values): byte, short, int,long, float, double, char, boolean 0121

22. Range of values allowed  Values stored by integer and floating point types: Note: float and double use scientific notation byte8 bits -128 127 short16 bits -32 768 32 767 int32 bits -2 147 483 648 2 147 483 647 long64 bits -9 223 372 036 854 775 808 9 223 372 036 854 775 807 double 64 bits +/- 4.9 E-324 +/- 1.8 E+308 TypeSizeMinimum ValueMaximum Value float32 bits +/- 1.4 E-45 +/- 3.4 E+38 0122

23. Declare and initialise a variable  Java is a statically typed language.  the association between a variable and the type of object the variable can refer to is determined when the variable is declared  Once the declaration is made it is an error for a variable to refer to an object of any other type. X 3 int x = 3; int x; x = 3; int x; x = 3; double percentagePassing101, percentagePassing105; boolean isTheLectureOverYet; x = 3.5; 0123

24. Printing variables  A variable can be used anywhere that a literal can be used.  We can print out the value stored in a variable using the System.out.println() statement, e.g.  Or using System.out.print()  Note: The println method prints a string and adds a newline character at the end. 23 number System.out.println(number); int number = 23; System.out.println(number); int number = 23; System.out.println(number); int number = 23; System.out.print("Hello World!"); System.out.print(number); int number = 23; System.out.print("Hello World!"); System.out.print(number); Hello World!23 int number = 23; System.out.println("Hello World!"); System.out.println(number); int number = 23; System.out.println("Hello World!"); System.out.println(number); Hello World! 23 Hello World! 23 0124

25. Symbolic constants – final  A symbolic constant is like a variable, except that the value it stores cannot change once it is initialised.  Use the following style guidelines for naming symbolic constants:  use all upper case letters  separate multiple words with an underscore final int DAYS_IN_YEAR = 365; final double GST_RATE = 0.125; final int DAYS_IN_YEAR = 365; final double GST_RATE = 0.125; DAYS_IN_YEAR = 30; 0125

26. Strings  Python:  String literals are formed using either the single quotes or the double quotes as delimiters.  Java:  String literals are formed using the double quotes as delimiters.  Character literals are formed using the single quotes as delimiters.  Java strings do not support a slicing operator.  Java uses method calls where Python uses Operators. PythonJavaDescription str[3]str.charAt(3)Return character in 3rd position str[2:5]str.substring(2,5)Return substring from 2nd to 4th len(str)str.length()Return the length of the string str.find('x')str.indexOf('x')Find the first occurrence of x str.split()str.split('\s')Split the string on whitespace into a list/array of strings str.split(',') Split the string at ',' into a list/array of strings str + strstr.concat(str)Concatenate two strings together str.strip()str.trim()Remove any whitespace at the beginning or end String greeting = "Hello World!"; char c = 'H'; String greeting = "Hello World!"; char c = 'H'; 0126

27. String Concatenation  Both Python and Java use the concatenation operator + to join two strings to form a third, new string  Python:  Operands of other types must be converted to strings before they can be concatenated  Java:  If one of the operands is a string, the other operand can be of any type. result = "35" + " pages long." result = str(35) + " pages long." result = "35" + " pages long." result = str(35) + " pages long." String result; result = "35" + " pages long." ; result = 35 + " pages long."; String result; result = "35" + " pages long." ; result = 35 + " pages long."; 0127

28. Type Conversion  Python:  Numeric types can be converted to other numeric types by using the appropriate type conversion functions. The function’s name is the name of the destination type.  Java:  Numeric types can be converted to other numeric types by using the appropriate cast operators. A cast operator is formed by enclosing the destination type name in parentheses. int(3.14) float(3) int(3.14) float(3) int x = (int) 3.14; double y = (double) 3; char p = (char) 65; int q = (int) 'a'; int x = (int) 3.14; double y = (double) 3; char p = (char) 65; int q = (int) 'a'; 3 3.0 A 97 3 3.0 A 97 0128

29. import  Python:  A module is imported using the form:  Java:  A package resource is imported using the form:  The resource is then referenced without the package name as a qualifier. import from import import from import import. ; import math print(math.sqrt(2), math.pi) import math print(math.sqrt(2), math.pi) import java.util.*;... ArrayList names = new ArrayList (); import java.util.*;... ArrayList names = new ArrayList (); 0129

30. The Random class  A Random object generates pseudo-random numbers.  Class Random is found in the java.util package.  Examples:  To get a random number from 0 to 9 inclusive  To get a number in arbitrary range [min, max] inclusive: Method nameDescription nextInt(max)returns a random integer in the range [0, max) in other words, 0 to max-1 inclusive nextDouble()returns a random real number in the range [0.0, 1.0) Random rand = new Random(); int randomNumber = rand.nextInt(10); Random rand = new Random(); int randomNumber = rand.nextInt(10); Random rand = new Random(); int size_of_range = max - min + 1; int n = rand.nextInt(size_of_range) + min; Random rand = new Random(); int size_of_range = max - min + 1; int n = rand.nextInt(size_of_range) + min; 0130

31. Lists Vs Arrays  Arrays In Java:  It is a sequence of elements of the same type.  Each element is accessed in constant time using an index position.  Unlike a list, an array’s length is fixed when it is created and cannot be changed.  Moreover, the only operations on an array are access or replacement of elements via subscripts.  Like other data structures, arrays are objects and thus are of a reference type.  The type of an array is determined by its element type, which is specified when the array is instantiated.  Default values:  Each array element in ages (int) has a default value of 0.  Each array element in names (string) has a default value of null  The length of an array can be obtained from the array object’s length variable  for loop can be used just to reference the elements in an array: int[] ages = new int[10]; String[] names = new String[10]; int[] ages = new int[10]; String[] names = new String[10]; System.out.println(names.length); for (String name: names) System.out.println(name); System.out.println(names.length); for (String name: names) System.out.println(name); ages[0] = 21; +ve index only 0131

32. ArrayLists  Lists in Python:  A list is a mutable sequence of 0 or more objects of any type.  The len function returns the number of elements in a list.  The subscript operator ([]) accesses an element at a given position. (+ve or –ve index)  ArrayLists in Java:  The type is determined when the ArrayList is instantiated.  Examples:  Names can contain only strings, whereas the second ArrayList can contain only instances of class Integer.  The class Integer is a wrapper class, which allows values of type int to be stored in an ArrayList.  When an int is inserted, the JVM wraps it in an Integer object. When an Integer object is accessed, the int value contained there is returned. ArrayList names = new ArrayList (); ArrayList ages = new ArrayList (); ArrayList names = new ArrayList (); ArrayList ages = new ArrayList (); ages.add(63); ages.set(0, ages.get(0) + 1); ages.add(63); ages.set(0, ages.get(0) + 1); +ve index only 0132

33. Boolean and Relational, Logical Operators  The type boolean includes the constant values true and false  The relational operators are ==, !=,, =.  The logical operators:  Python:  The logical operators are not, and, and or  Comparison operators can be chained  Java:  The logical operators are ! (not) && (and), and || (or). value > 10 and value < 100 10 < value < 100 value > 10 and value < 100 10 < value < 100 value > 10 && value < 100 value >= 10 || value == 5 value > 10 && value < 100 value >= 10 || value == 5 0133

34. Control Flow  Conditionals  Conditional statements in Python and Java are very similar  Simple if  if-else  The statements in the consequent and each alternative are marked by curly braces ({}). When there is just one statement, the braces may be omitted.  Each Boolean expression is enclosed in parentheses. if condition: statement1... if condition: statement1... if (condition) { statement1;... } if (condition) { statement1;... } if condition: statement1... else: statement1... if condition: statement1... else: statement1... if (condition) { statement1;... } else { statement1;... } if (condition) { statement1;... } else { statement1;... } 0134

35. Control Flow (con’t)  Conditionals  Nested if-else if grade < 60: print 'F' elif grade < 70: print 'D' elif grade < 80: print 'C' elif grade < 90: print 'B' else: print 'A' if grade < 60: print 'F' elif grade < 70: print 'D' elif grade < 80: print 'C' elif grade < 90: print 'B' else: print 'A' if (grade < 60) { System.out.println('F'); } else if (grade < 70) { System.out.println('D'); } else if (grade < 80) { System.out.println('C'); } else if (grade < 90) { System.out.println('B'); } else System.out.println('A'); if (grade < 60) { System.out.println('F'); } else if (grade < 70) { System.out.println('D'); } else if (grade < 80) { System.out.println('C'); } else if (grade < 90) { System.out.println('B'); } else System.out.println('A'); 0135

36. Control Flow  Loops  for + range (Python)  The variable picks up the value of each element in the iterable object and is visible in the loop body  The range function provides you with a wide variety of options for controlling the value of the loop variable  for (Java)  The Java for loop is really analogous to the last option giving you explicit control over the starting, stopping, and stepping in the three clauses inside the parenthesis. for i in range(10): print i for i in range(10): print i for (start clause; stop clause; step clause) { statement1;... } for (start clause; stop clause; step clause) { statement1;... } range(stop) range(start,stop) range(start,stop,step) range(stop) range(start,stop) range(start,stop,step) for (int i = 0; i < 10; i++){ System.out.println(i); } for (int i = 0; i < 10; i++){ System.out.println(i); } Note: “i” is only visible within the loop 0136

37. Control Flow  for - visiting each element in an iterable object  Python:  Java:  while:  do-while: This ensures that a loop will be executed at least one time for in :... for in :... for ( : ){ ;... } for ( : ){ ;... } for s in aListOfStrings: print(s) for s in aListOfStrings: print(s) for (String s : aListOfStrings){ System.out.println(s); } for (String s : aListOfStrings){ System.out.println(s); } while condition: statement1 statement2... while condition: statement1 statement2... while (condition) { statement1; statement2;... } while (condition) { statement1; statement2;... } do { statement1; statement2;... } while (condition); do { statement1; statement2;... } while (condition); 0137

38. File I/O  Python:  The input function displays its argument as a prompt and waits for input  When the user presses the Enter or Return key, the function returns a string representing the input text.  Java:  The Scanner class is used for the input of text and numeric data from the keyboard.  The programmer instantiates a Scanner and uses the appropriate methods for each type of data being input. name = input("Enter your name: ") age = int(input("Enter your age: ")) name = input("Enter your name: ") age = int(input("Enter your age: ")) Scanner in = new Scanner(System.in); fahr = in.nextDouble(); Scanner in = new Scanner(System.in); fahr = in.nextDouble(); Return typeMethod NameDescription booleanhasNext()returns true if more data is present booleanhasNextInt()returns true if the next thing to read is an integer Stringnext()returns the next thing to read as a String intnextInt()returns the next thing to read as an integer … 0138

39. Example:  Your BMI (body mass index) is considered healthy if it is in the range 19 – 25. Write a program that prompts the user to enter their height and weight.  Your program should then calculate the user’s BMI using the following formula:  Use Math.pow() to square the height. public class ExampleApp { public static void main(String[] args) { MyExample p = new MyExample(); p.start(); } public class ExampleApp { public static void main(String[] args) { MyExample p = new MyExample(); p.start(); } import java.util.Scanner; public class MyExample { public void start() { Scanner in = new Scanner(System.in); System.out.print("Enter your weight in kgs: "); double weight = in.nextDouble(); System.out.print("Enter your height in metres: "); double height = in.nextDouble(); double bmi = weight / (height * height); System.out.print("Your BMI is: "); System.out.println(bmi); } import java.util.Scanner; public class MyExample { public void start() { Scanner in = new Scanner(System.in); System.out.print("Enter your weight in kgs: "); double weight = in.nextDouble(); System.out.print("Enter your height in metres: "); double height = in.nextDouble(); double bmi = weight / (height * height); System.out.print("Your BMI is: "); System.out.println(bmi); } Enter your weight in kgs: 61.45 Enter your height in metres: 1.64 Your BMI is: 22.84726353361095 Enter your weight in kgs: 61.45 Enter your height in metres: 1.64 Your BMI is: 22.84726353361095 0139

40. Arguments for the method main  The heading for the main method shows a parameter that is an array of Strings:  When you run a program from the command line, all words after the class name will be passed to the main method in the args array.  The following main method in the class TestArray will print out the first two arguments it receives: public static void main(String[] args) {... } public static void main(String[] args) {... } >java TestArray Hello World public static void main(String[] args) { for (int i=0; i<args.length; i++) System.out.println(args[i]); } public static void main(String[] args) { for (int i=0; i<args.length; i++) System.out.println(args[i]); } >java TestArray Hello World Hello World >java TestArray Hello World Hello World Output: public static void main(String[] args) {... } public static void main(String[] args) {... } >java TestArray Hello World public static void main(String[] args) { for (int i=0; i<args.length; i++) System.out.println(args[i]); } public static void main(String[] args) { for (int i=0; i<args.length; i++) System.out.println(args[i]); } 0140

41. Multidimensional Arrays  Multidimensional Arrays  Arrays with more than one index  number of dimensions = number of indexes  Multidimensional arrays in Java are implemented as arrays of arrays  Examples:  Two-dimensional arrays  A two-dimensional array can be thought of as a table of values, with rows and columns  A two-dimensional array element is referenced using two index values  Example: int[][][] threeD = new int [2][3][4]; int[][][][] fourD = new int [2][3][768][1024]; int[][][] threeD = new int [2][3][4]; int[][][][] fourD = new int [2][3][768][1024]; int[][] x = new int[5][7]; 7 columns: 5 rows 0141

42. 2-Dimensional Arrays 123 456  Declaration & Initialization 2-D arrays  Syntax for 2-D arrays is similar to 1-D arrays  [][] = new [rows][columns];  Example 1:  The array should have five rows and seven columns  The real picture:  Example 2:  The array has 4 rows.  2-D Array Initializer  You can also initialize at declaration with 2D array literal  Use nested comma separated lists, enclosed in {}’s int[][] x = new int [4][]; int[][] x = new int[5][7]; int[][] y = { {1,2,3}, {4,5,6}}; 0142

43. Creating Multidimensional Arrays  We can use existing arrays for initialization  a3 does not store copies of a1 and a2 in Array3[0] and a3[1] respectively  Instead it stores reference to a1 and a2  If we change the value of a1[1], we also change the value of a3[0][1]  To create copies of an existing 1-dimensional arrays, we can use the clone method int[] a1 = {10,12,14}; int[] a2 = {20,22,24}; int[][] a3 = {a1, a2}; int[] a1 = {10,12,14}; int[] a2 = {20,22,24}; int[][] a3 = {a1, a2}; a1[1] = 0; System.out.println(a3[0][1]); a1[1] = 0; System.out.println(a3[0][1]); int[][] a4={a1.clone(), a2.clone()}; 010 112 214 a1 020 122 224 a2 0 1 a3 0 1 101214 202224 a4 010 112 214 a1 020 122 224 a2 0143

44. Length Variables  Syntax:  arrayName.length  returns the number of rows in the array  arrayName[rowToGet].length  returns the number of columns in row “rowToGet”  Note:  If x is a rectangular array, all rows have the same length int[][] x = new int[5][7]; System.out.println(x.length); System.out.println(x[0].length); int[][] x = new int[5][7]; System.out.println(x.length); System.out.println(x[0].length); 5757 Output: System.out.println(x[0].length); System.out.println(x[1].length); System.out.println(x[2].length); System.out.println(x[0].length); System.out.println(x[1].length); System.out.println(x[2].length); 777777 Output: 0144

45. Using 2D Arrays  Accessing elements  To access elements, we use pretty much the same technique as a 1D array  Initialization & Printing  Nested loops are used to initialize array elements and print out values  Algorithm:  Starting from the first row (0 th ) to the last row (n-1) – outer loop  For each row, starting from the first column (0 th ) to the last column (m-1) – inner loop  Print out the value int[][] y = { {1,2,3}, {4,5,6}}; for (int row = 0; row < y.length; row++) { for (int col = 0; col < y[row].length; col++) System.out.print(y[row][col] + " "); System.out.println(); } int[][] y = { {1,2,3}, {4,5,6}}; for (int row = 0; row < y.length; row++) { for (int col = 0; col < y[row].length; col++) System.out.print(y[row][col] + " "); System.out.println(); } System.out.println(myArr[rowToGet][colToGet]); Use y.length to navigate the last row Use y[row].length to navigate the last column of each row 0145

46. Cloning of Multi-D Arrays  It is shallow clone only  Remember that multi-dimensional arrays in Java are arrays of arrays. Cloning only generates a copy of the root array  Note: a5[0] and a5[1] from an 1-dimensional array that store the memory location m0 and m1 of two 1-dimensional arrays. If we clone a5, then we only create a new 1- dimensional array that stores m0 and m1. int[][] a5 = {{10,12,14}, {20,22,24}}; int[][] a6 = a5.clone(); int[][] a5 = {{10,12,14}, {20,22,24}}; int[][] a6 = a5.clone(); 0 1 a5 0 1 101214 202224 a6 0146

47. Ragged Arrays 32  Ragged arrays have rows of unequal length  Each row has a different number of columns, or entries  Declaration & Initialization a ragged array  Syntax:  [][] = new [rows][];  [0] = new [colCountForRow1]; ...  Array Initializer 0 1 2 int[][] b = {{3,2}, {3,2,1}, {1}}; int[][] b; b = new int[3][]; b[0] = new int[2]; b[1] = new int[3]; b[2] = new int[1]; int[][] b; b = new int[3][]; b[0] = new int[2]; b[1] = new int[3]; b[2] = new int[1]; 321 1 0 1 2 00 000 0 b b 0147

48. Using Ragged Arrays  Length Variables:  arrayName.length returns the number of rows in the array  arrayName[rowToGet].length returns the number of columns in row “rowToGet”  Example:  b.length = 3  b[0].length returns 2  b[1].length returns 3  b[2].length returns 1  b[3].length <- ERROR  Initialization & Printing  Nested loops are used to initialize array elements and print out values  Note: You must use y[row].length to get the number of columns in each row. The number may not be the same for all rows. for (int row = 0; row < y.length; row++) { for (int col = 0; col < y[row].length; col++) System.out.print(y[row][col] + " "); System.out.println(); } for (int row = 0; row < y.length; row++) { for (int col = 0; col < y[row].length; col++) System.out.print(y[row][col] + " "); System.out.println(); } int[][] y = {{3,2}, {3,2,1}, {1}}; 0148