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***** SWTJC STEM *****. Java Class Libraries & API’s. A class library is a set of classes that supports the development of programs. Java comes with a standard class library , but libraries can be obtained separately from third party vendors.

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Java class libraries api s l.jpg

***** SWTJC STEM *****

Java Class Libraries & API’s

  • A class libraryis a set of classes that supports the development of programs.

  • Java comes with a standard class library, but libraries can be obtained separately from third party vendors.

  • Classes in class libraries contain methods that are valuable to the programmer.

  • API’s (Application Programming Interfaces) are clusters of related classes.

    • Java Database API contains classes that help programmers use databases

    • Java Swing API contains classes that help programmers use graphical components.

Chapter 3-1 cg 36


Java packages l.jpg

***** SWTJC STEM *****

  • Classes are also grouped in packages.

  • Packages are more fundamental and language based than API’s.

  • See text appendix “M” for classes and packages.

  • Example packages from Java’s standard class library:

Java Packages

Chapter 3-1 cg 36


Java class packages l.jpg

***** SWTJC STEM *****

Java Class Packages

  • To use a package in a program, it must first beimported.

  • Add the import declaration at the beginning of a program, after the package statement and before any other executable code.

    • import packageName.*;Imports all classes inpackageName.

    • import packageName.classNameImports on className from packageName

      • Example: import java.text.DecimalFormat;Imports only the DecimalFormatclass from the java.text package.

  • The java.lang package does not have to be imported.

    • String and Mathmethods are always available.

Chapter 3-1 cg 36-37


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***** SWTJC STEM *****

Declaring An Object

  • To declare an object, use this statement:ClassName objectName = new ClassName (parameters);

  • Where:

    • ClassName is the name of the class of the object.

    • objectName is your choice of name for the variable object.

    • “=“ is the assignment operator.

    • new is a Java reserved word.

    • ( parameters) is a set of data values use to initialize or setup the object.

  • Except for Math class objects, all others must be declared before they are used.

Chapter 3-1 cg 36-37


String class l.jpg

***** SWTJC STEM *****

  • The String class provides a convenient way to manage and manipulate text.

  • The String class is in the java.lang package and is automatically imported.

  • See the chart below for a partial summary of available methods or appendix “M” for a complete list:

String Class

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String class ex l.jpg

***** SWTJC STEM *****

  • Example from Program “StringMutation” (See text CDROM Chapter 3)

String Class Ex.

  • // Variable object declaration

  • String phrase = "Change is inevitable";

  • String mutation1, mutation2, mutation3, mutation4;

  • System.out.println ("Original string: \"" + phrase + "\"");

    • System.out.println ("Length of string: " + phrase.length());... Outputs

    • Original string: "Change is inevitable"

    • Length of string: 20

Chapter 3-1 cg 35


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***** SWTJC STEM *****

  • Example from Program “StringMutation” (See text CDROM Chapter 3)

String Class Ex.

mutation1 = phrase.concat (", except from vending machines.");

mutation2 = mutation1.toUpperCase();

mutation3 = mutation2.replace ('E', 'X');

mutation4 = mutation3.substring (3, 30);

...Outputs

Mutation #1: Change is inevitable, except from vending machines.

Mutation #2: CHANGE IS INEVITABLE, EXCEPT FROM VENDING MACHINES.

Mutation #3: CHANGX IS INXVITABLX, XXCXPT FROM VXNDING MACHINXS.

Mutation #4: NGX IS INXVITABLX, XXCXPT F

Chapter 3-1 cg 35


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***** SWTJC STEM *****

  • The Scanner class provides a convenient way to read input values of various types.

  • The Scanner class accepts input from various sources including the keyboard, a file, or a string.

  • Must be imported from java.util package

  • For keyboard, use “System.in” in the constructor.

  • See the chart below for a partial summary of available methodsor appendix “M” for a complete list:

Scanner Class

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***** SWTJC STEM *****

  • An object declaration looks like this: Scanner scan = new Scanner (System.in);

    • Declares a “new” object variable named “scan” (your choice of object variable name).

    • The Scanner class has a special constructor method that constructs or creates this new object.

    • The parameter “System.in” tells the constructor to use the PC’s keyboard to accept data entry.

  • The input stream may contain more than one data item, called a token.

  • Tokens are separated by white space, the default delimiter.

  • To change the delimiter use useDelimiter(String pattern).

    • Example: scan.useDelimiter(“,”); changes the delimiter to a comma.

Scanner Class

Chapter 3-1 cg 32


Scanner class ex 1 l.jpg

***** SWTJC STEM *****

  • Example Program “Echo” (See text CDROM Chapter 2)

Scanner Class Ex. 1

//******************************************************

// Echo.java Author: Lewis/Loftus

//

// Demonstrates the use of the nextLine method of the Scanner class

// to read a string of text from the user.

//******************************************************

import java.util.Scanner; // First import the Scanner class

Package

Class

Dot Operator

Chapter 3-1 cg 32


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***** SWTJC STEM *****

  • Example 1 Program “Echo”

Scanner Class Ex. 1

public class Echo

{

//-----------------------------------------------------------------

// Reads a character string from the user and prints it.

//----------------------------------------------------------------- public static void main (String[] args) {

String message;

Scanner scan = new Scanner (System.in);

// Class objectName = new Class (constructor parameters);

System.out.println ("Enter a line of text:");

message = scan.nextLine();

System.out.println ("You entered: \"" + message + "\"");

}

}

Object

Method

Chapter 3-1 cg 32


Scanner class ex 2 l.jpg

***** SWTJC STEM *****

  • Example 2 Program “CalculateSum”

  • Input tokens on separate line.

Scanner Class Ex. 2

import java.util.Scanner;

public class CalculateSum {

public static void main(String[] args) {

double firstNum, secondNum, sum;

Scanner scan = new Scanner(System.in);

System.out.println("Enter first number to add:");

firstNum = scan.nextDouble();

System.out.println("Enter second number to add:");

secondNum = scan.nextDouble();

sum = firstNum + secondNum;

System.out.println(firstNum + " + " + secondNum + " = " + sum );

}

}

Chapter 3-1 cg 32


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***** SWTJC STEM *****

  • Example 3 Program “CalculateSumMultiple”

  • Input tokens on same line with white space as delimiter.

Scanner Class Ex. 3

import java.util.Scanner;

public class CalculateSumMultiple {

public static void main(String[] args) {

double firstNum, secondNum, sum;

Scanner scan = new Scanner(System.in);

System.out.println("Enter first and second number to add:");

firstNum = scan.nextDouble();

secondNum = scan.nextDouble();

sum = firstNum + secondNum;

System.out.println(firstNum + " + " + secondNum + " = " + sum );

}

}

Chapter 3-1 cg 32


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***** SWTJC STEM *****

import java.util.Scanner;

public class Average2Nums {

public static void main(String[] args) {

int firstNum, secondNum;

double average;

Scanner scan = new Scanner(System.in);

System.out.println("Enter first number to average:");

firstNum = scan.nextInt();

System.out.println("Enter second number to average:");

secondNum = scan.nextInt();

average = (double) (firstNum + secondNum) / 2;

System.out.println("Average of " + firstNum + " and " +

secondNum + " is " + average );

}

}

Scanner Class Ex. 4

Designates the keyboard

Casts the sum to double before dividing by 2

Chapter 2 cg 16


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***** SWTJC STEM *****

import java.util.Scanner;

public class ConvertSeconds {

public static void main(String[] args) {

int totalSeconds, hours, minutes, seconds;

Scanner scan = new Scanner(System.in);

totalSeconds = scan.nextInt();

seconds = totalSeconds;

hours = seconds / 3600; // Integer division

seconds = seconds % 3600; //modulo

minutes = seconds / 60;

seconds = seconds % 60;

System.out.println(totalSeconds + " sec is " + hours + " hours, " +

minutes + " minutes, and " + seconds + " seconds");

}

}

Scanner Class Ex. 5

Why?Becausehours & seconds are integer!

Chapter 2 cg 16