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The Random and String Classes

The Random and String Classes. The import statement. Creating Objects. A variable holds either a primitive type or a reference to an object Object objectName = new Object (0 or more parameters);. Object o; In the above declaration, what will be the value of o ? Object x; x=o;

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The Random and String Classes

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  1. TheRandom andStringClasses The import statement

  2. Creating Objects A variable holds either a primitive type or a reference to an object Object objectName = new Object (0 or more parameters); Object o; In the above declaration, what will be the value of o? Object x; x=o; Explain the above situation… Blanca Polo ICS111

  3. Question Object o; In the above declaration, what will be the value of o? Object x; x=o; Explain the above situation… Blanca Polo ICS111

  4. Invoking Methods returnValue =Object.method(parameters); Will I always have a return value? Are parameters always present? Blanca Polo ICS111

  5. ”Tom Hanks" name1 Before: ”Kurt Russell" name2 ”Tom Hanks" name1 After: name2 Aliases • Two or more references that refer to the same object are called aliases of each other name2 = name1; Blanca Polo ICS111

  6. Garbage Collection • When an object no longer has any valid references to it, it can no longer be accessed by the program • The object is useless, and therefore is called garbage • Java performs automatic garbage collection periodically, returning an object's memory to the system for future use • In other languages, the programmer is responsible for performing garbage collection Blanca Polo ICS111

  7. Class Libraries • A class library is a collection of classes that we can use when developing programs • The Java standard class library is part of any Java development environment • Other class libraries can be obtained through third party vendors, or you can create them yourself Blanca Polo ICS111

  8. What is in a Package • A package is a directory of files that contain utilities. • All classes of the java.lang package are imported automatically into all programs. • The String class, and the System.out class are part of this package. Blanca Polo ICS111

  9. Package java.lang java.applet java.awt javax.swing java.net java.util javax.xml.parsers Purpose General support Creating applets for the web Graphics and graphical user interfaces Additional graphics capabilities Network communication Utilities XML document processing Packages • The classes of the Java standard class library are organized into packages • Some of the packages in the standard class library are: Blanca Polo ICS111

  10. The import Declaration • When you want to use a class from a package, you could use its fully qualified name java.util.Random • Or you can import the class, and then use just the class name import java.util.Random; • To import all classes in a particular package, you can use the * wildcard character import java.util.*; Blanca Polo ICS111

  11. The import Declaration • Import statements are always at the top of the program. import java.lang.*; • Many of the classes that we will use in this class will need to be imported. • Different JAVA programming environments have different libraries • We will use the standard libraries that can be found in any programming environment. Blanca Polo ICS111

  12. Counting JAVA is zero based Blanca Polo ICS111

  13. The Random Class • The Random class is part of the java.util package • It provides methods that generate pseudorandom numbers Blanca Polo ICS111

  14. Random Class Methods • Constructor: Random( ) Random r = new Random( ); • float nextFloat( ) • Returns a random number between • 0.0 and 1.0 inclusive • float f; • f = r.nextFloat( ); Blanca Polo ICS111

  15. More Random Class Methods • int nextInt( ) • Returns a random number that • ranges over all possible int values • positive and negative • int i; • i = r.nextInt( ); • int nextInt( int num ) • Returns a random number between • 0 and num-1 (inclusive) • int i; • i = r.nextInt(5 ); • // generates a number between 0 and 4 See Java/Numbers/GenOneRandom.java Java/Numbers/OneRandom.java Blanca Polo ICS111

  16. String Methods • Once a String object has been created, neither its value nor its length can be changed. Thus we say that an object of the String class is immutable • However, several methods of the String class return new String objects that are modified versions of the original Blanca Polo ICS111

  17. String Indexes String s = “Hello world”; • The length of s is 11 • It has positions from 0 to 10 Blanca Polo ICS111

  18. String Methods • String toUpperCase( ) • String toLowerCase( ) • int length( ) • String substring(int begin) • String substring(int begin, int end) • String replace( char oldChar, char newChar) • String trim( ) • int indexOf(char anyChar) • int indexOf(String anyString) • char charAt(int position) • String concat(String anotherString) Blanca Polo ICS111 See java/String/StringMethods.java

  19. Questions? import Method calling Random String Return values Blanca Polo ICS111

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