Presentation is loading. Please wait.

Presentation is loading. Please wait.

An Introduction to Java – Part 1 Erin Hamalainen CS 265 Sec 001 October 20, 2010.

Similar presentations


Presentation on theme: "An Introduction to Java – Part 1 Erin Hamalainen CS 265 Sec 001 October 20, 2010."— Presentation transcript:

1 An Introduction to Java – Part 1 Erin Hamalainen CS 265 Sec 001 October 20, 2010

2 Some Java Basics Derives most of its syntax from C++ Built almost exclusively as an object- oriented programming language All code is written inside a class Everything is an object, with the exception of the intrinsic data types

3 Data Types (also called primitive types) Byte –Min value: -128 –Max value: 127 –8 bits (used for memory saving purposes) Short –Min value: -32,768 –Max value: 32,767 –16 bits Int –Min value: -2,147,483,648 –Max value: 2,147,483,647 –32 bits –For integral types, this data type is generally the default Long –Min value: -9,223,372,036,854,775,808 –Max value: 9,223,372,036,854,775,807 –64 bits –Use this only when you need a range of values wider than those provided by int

4 Data Types (also called primitive types) Float –Use a float (instead of a double) if you need to save memory –Single precision, 32 bit Double –For decimal values this is the default choice –Double precision, 64 bit Boolean –Two possible values: true and false Char –A single character

5 Arrays A container object that holds a fixed number of values of a single type Length is established when the array is created. After creation, length is fixed. Declaration: int[] anArray; // declares an array of integers The declaration does not actually create an array. It simply tells the compiler that this variable will hold an array of the specified type.

6 Arrays cont’d You can also declare an array like this: int anArray[]; //this form is discouraged However, convention discourages this form; the brackets identify the array type and should appear with the type designation. int[] anArray;//declares an array of integers anArray = new int[10]; //allocates memory for 10 integers Alternatively you can use the shortcut syntax to create and initialize an array int[] anArray = {1,2,3,4,5,6,7,8,9,10}; Here the length of the array is determined by the number of values between { and }.

7 Arrays cont’d Elements of an array are accessed using subscripts (just like in C++ and Perl) int[] anArray; //declares an array of integers anArray = new int[10];//allocates memory for 10 integers anArray[0] = 1;//initialize first element anArray[1] = 2;//Initialize second element System.out.println(“Element at index 0: “ + anArray[0]); System.out.println(“Element at index 1: “ + anArray[1]);

8 Selected Member Functions for Arrays Static void sort(type[] a) –Sorts an array using a QuickSort algorithm Static int binarySearch(type[] a, type v) –Argument a is a sorted array. This function searches for v among the elements of a and returns subscript if v is found. Static boolean equals(type[] a, Object other) –This function returns true if other is an array of the same type as a, if it has the same length, and if the corresponding elements match

9 Strings Strings are a standard class in Java String str1; //declare a string variable str1 = “Erin”; //initialize string variable String str2 = “My name is” //declaration and initialization in one line String concatenation: + String str3 = str2 + “ “ + str1 + “.”; //str3 holds the string “My name is Erin.”

10 Selected Member Functions for Strings int compareTo(String other) –Returns a negative value if the implicit argument comes before the explicit argument, a positive value if the explicit argument comes before the implicit argument, and 0 if the strings are equal int cmp = impStr.compareTo(expStr); boolean equals(Object other) –Returns true if the implicit argument equals the explicit argument. Returns false otherwise. boolean eq = impStr.equals(expStr); int length() –Returns the length of the string int length = impStr.length();

11 Operators Arithmetic Operators +, -, *, /, % Relational Operators ==, !=,, = Logical Operators &&, ||, !

12 Control Flow If else statements –Same as in C++ –Curly braces are unnecessary if they only enclose one statement While loops –Same as C++ –Curly braces are unnecessary if they only enclose one statement For loops –Same as C++ for(int i=0; i<5; i++) System.out.println(numbers[i]);

13 Program Structure Public class className { public static void main(String[] args) { program statements } user-defined methods } Public classes are accessible from any class Classes that are not declared public are accessible only within their package –(A package is a namespace for organizing classes and interfaces in a logical manner. Placing your code into packages makes large software projects easier to manage. ) Public methods may be called from any class Static methods do not operate on objects The keyword void indicates that the method does not return a value The array args of the main method stores command line arguments

14 public class SortJava { public static void main(String[] args) { int n=5; int[] numbers = new int[n]; //The Math.random() method returns a random floating oint number in the range //[0,1). We multiply the random number by n and then we cast the type of the result //to integer. for(int i=0; i<numbers.length; i++) numbers[i]=(int)(Math.random()*n); System.out.println("Random numbers before sorting"); for(int i=0; i<numbers.length; i++) System.out.println(numbers[i]); System.out.println(); System.out.println("Random numbers after sorting"); // We call sort method of Arrays class. // Array class is located in java.util.Arrays. Import //statement java.util.* allows us to access it. Arrays.sort(numbers); for(int i=0; i<numbers.length; i++) System.out.println(numbers[i]); }

15 Source Code, Compilation, Execution Source code needs to have same as name of public class –There can only be one public class in a Java program Source code needs to have extension.java During compilation, the Java compiler produces a bytecode file –This file has the extension.class The Java interpreter starts execution when we type command java followed by the class name

16 Questions?


Download ppt "An Introduction to Java – Part 1 Erin Hamalainen CS 265 Sec 001 October 20, 2010."

Similar presentations


Ads by Google