cs111: programming language ii · · 2014-01-20text i/o standard output. flexible os abstraction...

CS111: PROGRAMMING

LANGUAGE II

Lecture 1(b): Java Basics (I) Computer Science

Department

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Lecture Contents

Computer Science Department

Java basics

Input/output

Variables

Expressions

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Your first Java program.. 3

// indicates a

comment.

class keyword

Java is case

sensitive

braces { , }

delimit a

class body

main Method


“Everything must be in a class”

There are no global functions or global data.

Basic language elements 4

Text I/O

Standard output.

Flexible OS abstraction for output.

In Java, applications use the standard output object

(System.out) to display text on terminal.


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Command line output 6

Multiple line

O/P

Formatting

output

public class TestIO {

public static void main(String[] args)

{

System.out.println(“Welcome to java”);

System.out.println(“Welcome to \n java”);

System.out.print(“Welcome to”);

System.out.println(“java”);

System.out.printf(“%s\n%s\n“, “Welcome

to”,”java”);

}

}

}


Common escape sequences


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Printf Conversion-Characters


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Strings & Text

String msg1 = new String( “Hello” );

String msg2 = “Hello” ;

String msg3 = “Year “ + 2005; //valid??

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Standard Input

input is received from Terminal window.

Input entered while program is executing.


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Reading values


use : import java.util.Scanner;

Define an object of the Scanner class:

Scanner input = new Scanner(System.in);

input values:

num1 = input.nextInt();

Display after calculation:

System.out.printf(“the square is : %d

\n”, num1*num1);

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example 12


example


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variables

Declaration, memory allocation, initialization

int total = 0;

int count, temp, result;

Multiple variables can be created in one declaration

data type variable name


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Constants


A “constant variable” is an identifier that is similar to a

variable except that it holds one value for its entire existence

Why constants:

give names to otherwise unclear literal values

facilitate changes to the code

prevent inadvertent errors

In Java:

final double PI = 3.14159265;

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Arithmetic Expressions

An expression is a combination of operators and operands

Arithmetic expressions (we will see logical expressions later)

are essentially special methods applied to numerical data

objects: compute numeric results and make use of the arithmetic

operators:

Addition +

Subtraction -

Multiplication *

Division /

Remainder %


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Assignment-related Operators

Increment and decrement operators: ++, --

Assignment operators: +=, -=, *=, /=

count = count + 1;

count += 1;

count ++;

count = count - 10;

count -= 10;

these three expressions have the same effect

these two expressions have the same effect


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Operator Precedence

What is the order of evaluation in the following expressions?

a + b + c + d + e

4 3 2

a + b * c - d / e

3 2 4 1

a / (b + c) - d % e

2 3 4 1

a / (b * (c + (d - e)))

4 1 2 3

1


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How Do Data Conversions Happen?

Implicitly:

occurs automatically

uses widening conversion,

Examples: 4.0 / 8 (which / is it: double/double, float/float, int/int)

4 / 8.0 (which / is it: double/double, float/float, int/int)

4 + 5 / 9 + 1.0 + 5 / 9 / 10.0 (what is the value?)


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How Do Data Conversions Happen?


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Explicitly: Casting

widening / narrowing conversions

Examples: double MyResult;

MyResult = 12.0 / 5.0; //OK

int myInt = (int) MyResult; // truncation

MyResult = (double)myInt/3.0;

Be careful!!

Example: in 1996, Ariane 5 rocket exploded after

takeoff because of bad type conversion.


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Class Math

All Math class methods are static

Each is called by preceding the name of the method with the class name Math and the dot (.) separator

Method arguments may be constants, variables or expressions


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Computer Science Department 23

Example

Solve quadratic equation ax2 + bx + c = 0.

public class Quadratic {

public static void main(String[] args) {

double a,b,c,d;

// input coefficient values..

// calculate roots

d = Math.sqrt(b*b - 4.0*a*c);

double root1 = (-b + d) / (2.0*a);

double root2 = (-b - d) / (2.0*a);

// print them out

System.out.println(root1);

System.out.println(root2);

}

}


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Text Book:

Chap 2

That’s all for today…..


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cs111: programming language ii · · 2014-01-20text i/o standard output. flexible os abstraction...

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