Static Methods - Building Java Programs | CSE 142, Study notes of Linux skills

Download Static Methods - Building Java Programs | CSE 142 and more Study notes Linux skills in PDF only on Docsity!

Building Java ProgramsCopyright 2008 by Pearson Education

Chapter 1Lecture 1-2: Static Methods reading: 1.4 - 1.

Copyright 2008 by Pearson Education

Comments

^ comment

: A note written in source code by theprogrammer to describe or clarify the code.
Comments are not executed when your program runs.

^ Syntax:^ //^ comment text, on one line^ or,^ /*^ comment text; may span multiple lines

^ Examples:^ // This is a one-line comment./* This is a very longmulti-line comment. */

Copyright 2008 by Pearson Education Comments example / Suzy Student, CS 101, Fall 2019This program prints lyrics about ... something. / public class BaWitDaBa {public static void main(String[] args) { // first verse System.out.println("Bawitdaba");System.out.println("da bang a dang diggy diggy");System.out.println(); // second verse System.out.println("diggy said the boogy");System.out.println("said up jump the boogy");} }

Copyright 2008 by Pearson Education

Static methods^ reading: 1.4^ self-check: 16-25exercises: #5-10videos: Ch. 1 #

Copyright 2008 by Pearson Education Problems with algorithms
lack of structure

: Many tiny steps; tough to remember.

^ redundancy

: Consider making a double batch...

^ Mix the dry ingredients.
^ Cream the butter and sugar.
^ Beat in the eggs.
^ Stir in the dry ingredients.
^ Set the oven temperature.
^ Set the timer.
^ Place the first batch of cookies into the oven.
^ Allow the cookies to bake.
^ Set the timer.
^ Place the second batch of cookies into the oven.
^ Allow the cookies to bake.
^ Mix ingredients for frosting.
^ ...

Copyright 2008 by Pearson Education Structured algorithms
structured algorithm

: Split into coherent tasks.

1 Make the cookie batter.
^ Mix the dry ingredients.
^ Cream the butter and sugar.
^ Beat in the eggs.
^ Stir in the dry ingredients. 2 Bake the cookies.
^ Set the oven temperature.
^ Set the timer.
^ Place the cookies into the oven.
^ Allow the cookies to bake. 3 Add frosting and sprinkles.
^ Mix the ingredients for the frosting.
^ Spread frosting and sprinkles onto the cookies....

Copyright 2008 by Pearson Education A program with redundancy public^ class BakeCookies {public^ static

void^ main(String[] args)

System.out.println("Mix

the dry^ ingredients."); System.out.println("Cream

the butter^ and sugar."); System.out.println("Beat

in the^ eggs."); System.out.println("Stir

in the^ dry^ ingredients."); System.out.println("Set

the oven temperature."); System.out.println("Set

the timer."); System.out.println("Place

a batch of^ cookies into the

oven.");

System.out.println("Allow

the cookies to bake."); System.out.println("Set

the oven temperature."); System.out.println("Set

the timer."); System.out.println("Place

a batch of^ cookies into the

oven.");

System.out.println("Allow

the cookies to bake."); System.out.println("Mix

ingredients^

for frosting."); System.out.println("Spread frosting

and sprinkles.");

} }

Copyright 2008 by Pearson Education

Static methods

^ static method

: A named group of statements.

^ denotes the

structure^ of a program

^ eliminates^

redundancy^ by code reuse

^ procedural decomposition

dividing a problem into methods
Writing a static method is likeadding a new command to Java.

class method A
statement
statement
statement method B
statement
statement method C
statement
statement
statement

Copyright 2008 by Pearson Education Design of an algorithm // This program displays a delicious recipe

for baking^ cookies.

public^ class BakeCookies2 {public^ static

void^ main(String[] args)

//^ Step 1: Make the

cake^ batter. System.out.println("Mix

the dry^ ingredients."); System.out.println("Cream

the butter^ and sugar."); System.out.println("Beat

in the^ eggs."); System.out.println("Stir

in the^ dry^ ingredients."); //^ Step 2a: Bake cookies

(first^ batch). System.out.println("Set

the oven temperature."); System.out.println("Set

the timer."); System.out.println("Place

a batch of^ cookies into the

oven.");

System.out.println("Allow

the cookies to bake."); //^ Step 2b: Bake cookies

(second batch). System.out.println("Set

the oven temperature."); System.out.println("Set

the timer."); System.out.println("Place

a batch of^ cookies into the

oven.");

System.out.println("Allow

the cookies to bake."); //^ Step 3: Decorate

the^ cookies. System.out.println("Mix

ingredients^

for frosting."); System.out.println("Spread frosting

and sprinkles.");

} }

Copyright 2008 by Pearson Education

Gives your method a name so it can be executed
Syntax: public static void

name() {

Declaring a method statement; statement; ... statement; }
Example: public static void printWarning() { System.out.println("This product causes cancer");System.out.println("in lab rats and humans."); }

Copyright 2008 by Pearson Education Program with static method public^ class FreshPrince {public^ static

void^ main(String[] args)

rap();^

//^ Calling (running) the

rap method

System.out.println(); rap();^

//^ Calling the rap

method again

} //^ This^ method prints the lyrics to

my^ favorite song. public^ static

void^ rap()^ { System.out.println("Now

this is^ the^

story^ all^ about how"); System.out.println("My life got

flipped turned

upside-down");

} } Output: Now this is^ the story

all about^ how My life got^ flipped turned upside-downNow this is^ the story

all about^ how My life got^ flipped turned upside-down

Copyright 2008 by Pearson Education Final cookie program // This program displays a delicious recipe

for baking^ cookies.

public^ class BakeCookies3 {public^ static

void^ main(String[] args)

makeBatter();bake();^

// 1st^ batch bake();^

// 2nd^ batch decorate(); } // Step^ 1: Make the cake

batter. public^ static

void^ makeBatter() { System.out.println("Mix

the dry^ ingredients."); System.out.println("Cream

the butter^ and sugar."); System.out.println("Beat

in the^ eggs."); System.out.println("Stir

in the^ dry^ ingredients."); } //^ Step^ 2: Bake a

batch^ of cookies. public^ static

void^ bake() { System.out.println("Set

the oven temperature."); System.out.println("Set

the timer."); System.out.println("Place

a batch of^ cookies into the

oven.");

System.out.println("Allow

the cookies to bake."); } //^ Step^ 3: Decorate the

cookies. public^ static

void^ decorate()

System.out.println("Mix

ingredients^

for frosting."); System.out.println("Spread frosting

and sprinkles.");

} }

Copyright 2008 by Pearson Education

^ When a method is called, the program's execution...^
^ "jumps" into that method, executing its statements, then^
^ "jumps" back to the point where the method was called. public^ class

MethodsExample

public^ static

void^ main(String[]

args)^ {

message1();message2(); System.out.println("Done

with^ main.");

public static void message1()

{ System.out.println("This

is message1."); } public static void message2()

{ System.out.println("This

is message2."); message1(); System.out.println("Done

with^ message2."); } public static void message1()

{ System.out.println("This

is message1.");

Control flow }

Copyright 2008 by Pearson Education When to use methods
Place statements into a static method if:
The statements are related structurally, and/or
The statements are repeated.
You should not create static methods for:
An individual^ println

statement.

^ Only blank lines. (Put blank

printlns in

main.)

^ Unrelated or weakly related statements.(Consider splitting them into two smaller methods.)