1、Introduction to Computers and Programming Introduction to Methods in Java,Introduction to Computers and Programming in JAVA: V22.0002,Road Map,Introduction to Methods Divide and Conquer Abstraction Using Pre-Packaged Modules Understanding Method signatures Understanding java.lang.math methods Creati
2、ng your own methods,Introduction to Methods,4,6.1 Introduction,Modules Small pieces of a problem e.g., divide and conquer Facilitate design, implementation, operation and maintenance of large programs,5,6.2 Program Modules in Java,Modules in Java Methods (based on functions in procedural programming
3、) Classes (object oriented programming) Java API provides several modules that are already defined in java “system defined” Math.random() Programmers can also create their own modules e.g., programmer-defined methods Methods Invoked by a method call Returns a result to calling method (caller) Simila
4、r to a boss (caller) asking a worker (called method) to complete a task. The boss method delegates certain jobs to specific methods.,6,Fig. 6.1 Hierarchical boss-method/worker-method relationship.,Examples of methods,A method that determines the maximum of two numbers. A method that sorts a list of
5、names A method that opens a file from the file system. A method that reads from the open file. A method that opens a new socket to the internet. A method that reads from that socket.,Important concept #1,Divide and Conquer: Break large programs into a series of smaller modulesHelps manage complexity
6、 Makes it easier to build large programs Makes it easier to debug programs,Important concept #2,Methods provide: Abstraction (information hiding): Most of the time, you need to know what a function does, but not how it actually does it. Also helps manage complexity You use other peoples code without
7、 knowing how it does its job.,Using Static methods in the Java API,11,6.3 Math-Class Methods,Class java.lang.Math Provides common mathematical calculations Calculate the square root of 900.0: Math.sqrt( 900.0 ) Method sqrt belongs to class Math Dot (.) allows access to method sqrt The argument 900.0
8、 is located inside parentheses,Class,Method which belongs to class Math This always performs actions.,Parameters or data passed to method to perform an action,12,13,6.4 Methods Declarations,Methods Allow programmers to modularize programs Makes program development more manageable Software reusabilit
9、y Avoid repeating code Local variables Declared and used in method declaration (its scope is the method only) Parameters or arguments Communicates information between methods via method calls,14,6.4 Method Declarations (Cont.),Programmers can write customized methods,Line 9: method call to square li
10、ne 16: header for method square. States that we have a method that accepts one integer as a parameter and returns one integer line 18: returns the value y * y,1 / Fig. 6.3: SquareIntegers.java 2 / Creating and using a programmer-defined method. 3 public class SquareIntegers 4 public static void main
11、 (String args) 5 6 int result; / store result of call to method square7 / loop 10 times 8 for ( int counter = 1; counter = 10; counter+ ) 9 result = square( counter ); / method call10 / print the result of one call to the method 11 System.out.println (“The square of “ + counter + “ is “ + 12 result
12、);13 / end for 14 / end method main()15 / square method declaration 16 public static int square( int y ) 17 18 return y * y; / return square of y19 / end method square 20 / end class SquareIntegers,Modified by Evan Korth, 2003 Prentice Hall, Inc. All rights reserved.,16,6.4 Method Declarations (cont.),General format of method declaration: modifiers return-value-type method-name( parameter1, , parameterN ) declarations and statements Method can also return values:return expression;,
