Java(ch1)-Expression,ClassString
java is device independent
WORA : write once runs anywhere
other languages: procedure or function
java: method
Java application Programs
application- class with a method named main
applets(little java application)- run on web browser
public static void main(String[] args) : the main method
System.out - sending output to the screen
println - system.out使用方法
answer = 2 + 2; プラス記号
"2 plus 2 is"+ answer; 答えをstringに変換して貼り付け
High level language
Machine language
Assembly language (readable machine lan)
Compiler (high lev -> low lev translate)
source code(x.java) -> compiler ->
byte code(x.class) -> interpreter ->
->result on screen
Code
Source code
Object code (output of compiler)
linker in other programming lan
Syntax : grammar rules
Semantics : meaning of program
Bug: any/debugging: eliminating bug
syntax error: grammatical mistake
run-time error: error after executin (ex. 5/0)
logic errror : mistake in algorithm, not detected by compiler, but program not working
Expressions and Assignments
byte a = 10;
byte b = 20;
byte c = a + b ; ERROR(byte+byte -> int+int = int)
use ()s for safety!
base+rate * hours = base+(rate * hours)
n1=n2=n3 -> n1=(n2=n3)
String Class
WORA : write once runs anywhere
other languages: procedure or function
java: method
Java application Programs
application- class with a method named main
applets(little java application)- run on web browser
public class FirstProgram
{
public static void main (String[] args)
{
System.out.println("Hello World");
int answer;
answer = 2+2;
System.out.println("2 plus 2 is" + answer);
}
}
firstProgram : class namepublic static void main(String[] args) : the main method
System.out.println
System.out - sending output to the screen
println - system.out使用方法
= & +
answer = 2 + 2; プラス記号
"2 plus 2 is"+ answer; 答えをstringに変換して貼り付け
High level language
Machine language
Assembly language (readable machine lan)
Compiler (high lev -> low lev translate)
source code(x.java) -> compiler ->
byte code(x.class) -> interpreter ->
->result on screen
program terminology
Code
Source code
Object code (output of compiler)
class loader
linker in other programming lan
Syntax : grammar rules
Semantics : meaning of program
Type of Errors
Bug: any/debugging: eliminating bug
syntax error: grammatical mistake
run-time error: error after executin (ex. 5/0)
logic errror : mistake in algorithm, not detected by compiler, but program not working
Expressions and Assignments
Naming Convention
variables & methods (ex.int numberOfBeans)
camel case, start w/lowercase
classes (ex. FirstProgram)
start w/uppercase
primitive types
assignment statements
variable = expression;
with initialization
int count = 0;
double distance = 55 * .5;
char grade = 'A';
int initialCount = 50, finalCount; (初期値は50、finalもint)
assignment compatibility
byte,char < short < int < long < float < double
int x = (int)3.5;
=>x=3
double a = 5.89e-4;
char c = 'z';
String str = "hello world";
long f = 50000000000000L;
boolean d = true;
byte b = 20;
byte c = a + b ; ERROR(byte+byte -> int+int = int)
precedence and associativity rules
use ()s for safety!
base+rate * hours = base+(rate * hours)
n1=n2=n3 -> n1=(n2=n3)
increment and decrement operators
int n = 2;
int m = 2 * (++n); //prefix increment of n
System.out.println(m); //6
System.out.println(n); //3
int n = 2;
int m = 2 * (n++); //postfix increment of n
System.out.println(m); //4
System.out.println(n); //3
String Class
no primitive type for string in JavaString str1 = "hello";
String str2 = "world";
String str3 = str1 + " " + str2; // hello world
int k = 35;
String str4 = "yes" + k ; // yes35
classes, objects, methods
class
name of type whose values are objects
objects ex) System.out
entities that store data and take actions
instance of class type
methods ex) println
the action that an object can take
methods can return a value
objects within a same class has same object, different value
calling a method
System.out.println(...)
String Methods
int length() String greeting = "Hello";
int count = greeting.length(); //5
System.out.println("Length is " + greeting.length()); // Length is 5
boolean equals(Other_String) String greeting = "Hello";
greeting.equeals("hello"); //returns false
boolean equalsIgnoreCase(Other_string)String greeting = "Hello";
greeting.equeals("hello"); //returns true
String toLowerCase() String toUpperCase()String greeting = "Hi Mary!";
greeting.toLowercase(); //returns "hi mary!";
greeting.toUppercase(); //returns "HI MARY!";
String trim()String pause = " Hmm ";
pause.trim() // returns "Hmm"
char charAt(Position)String greeting = "Hello!";
greeting.charAt(0); // H
String substring(Start (,End))String sample = "AbcdEFG";
sample.substring(2); // cdEFG
sample.substring(3,6); // dEF
int indexOf(A_String) String greeting = "Hi Mary" ;
greeting.indexOf("Mary"); // 3
greeting.indexOf("Sally"); // -1
int compareTo(A_String)
int compareToIgnoreCase(A String)辞書(小文字<<大文字)String entry = "adventure";
entry.compareTo("zoo"); // 사전식 뒤 -> returns negative num
entry.compareTo("adventure") // 동일 0
entry.compareTo("above"); // 사전식 앞 -> returns positive num
entry.compareToIgnoreCase("Zoo") // negative
entry.compareToIgnoreCase("ADVENTURE") // 0
escape sequences\" \' \\ \n \r \t
ASCII
UNICODE
a character set used by the Java language
ASCII+言語で使用される多くの文字(英語/韓国語/中...)2bytes(16bits)
名前Constants Cと同じ
classで設定し、変更しない変数public static final int INCHES_PER_FOOT = 12;
public static final double RATE = 2.5 ;
comments C++と同じ//주석주석
/* 주석주석 */
javadoc /** automatically extract documentation from block comments in the classes
いいハーモニー!
self-documenting
right choice of identifier names
good indenting pattern
Reference
この問題について(Java(ch1)-Expression,ClassString), 我々は、より多くの情報をここで見つけました
https://velog.io/@yungommi/객체지향프로그래밍1
テキストは自由に共有またはコピーできます。ただし、このドキュメントのURLは参考URLとして残しておいてください。
Collection and Share based on the CC Protocol
String str1 = "hello";
String str2 = "world";
String str3 = str1 + " " + str2; // hello world
int k = 35;
String str4 = "yes" + k ; // yes35
String greeting = "Hello";
int count = greeting.length(); //5
System.out.println("Length is " + greeting.length()); // Length is 5
String greeting = "Hello";
greeting.equeals("hello"); //returns false
String greeting = "Hello";
greeting.equeals("hello"); //returns true
String greeting = "Hi Mary!";
greeting.toLowercase(); //returns "hi mary!";
greeting.toUppercase(); //returns "HI MARY!";
String pause = " Hmm ";
pause.trim() // returns "Hmm"
String greeting = "Hello!";
greeting.charAt(0); // H
String sample = "AbcdEFG";
sample.substring(2); // cdEFG
sample.substring(3,6); // dEF
String greeting = "Hi Mary" ;
greeting.indexOf("Mary"); // 3
greeting.indexOf("Sally"); // -1
String entry = "adventure";
entry.compareTo("zoo"); // 사전식 뒤 -> returns negative num
entry.compareTo("adventure") // 동일 0
entry.compareTo("above"); // 사전식 앞 -> returns positive num
entry.compareToIgnoreCase("Zoo") // negative
entry.compareToIgnoreCase("ADVENTURE") // 0
\" \' \\ \n \r \t
public static final int INCHES_PER_FOOT = 12;
public static final double RATE = 2.5 ;
//주석주석
/* 주석주석 */
/** automatically extract documentation from block comments in the classes
Reference
この問題について(Java(ch1)-Expression,ClassString), 我々は、より多くの情報をここで見つけました https://velog.io/@yungommi/객체지향프로그래밍1テキストは自由に共有またはコピーできます。ただし、このドキュメントのURLは参考URLとして残しておいてください。
Collection and Share based on the CC Protocol