Screen output

println 줄바꿈
print 다붙여씀

printf : format str + output str
%f - float %d - integer %s - string %e

System.out.print("$");
System.out.printf("%10.4f", 23.788888); 
System.out.println("each");
System.out.printf("Start%-8.2fEnd%n", 12.123);
System.out("$%6.2f_%d for each %s.%n", 19.8, 3, "apple"); 
System.out.printf("%2s%n","zzzzz");
System.out.printf("%7c%n","z");
System.out.printf("%12.5e", 123456.1234567);

//$___23.7889each
Start12.12___End
$_19.80_3 for each apple.
zzzzz 
______z
__1.2346e+05

M.Nf => M자리차지 N소수점아래
string은 생략 안함
e 디폴트: 1.123456e+0n 소수점6개

System.out
Class system
an object used for sending output to the screen

println
method that System.out object performs

Money Formats
import java.text.NumberFormat
getCurrencyInstance(나라, 디폴트는 현재나라);

import java.text.NumberFormat; 
import java.util.Locale; 

NumberFormat moneyFormater = NumberFormat.getCurrencyInstance();
System.out.println(moneyFormater.format(23.5));
NumberFormat dollarFormater = NumberFormat.getCurrencyInstance(Locale.US);
System.out.println(dollarFormater.format(23.5));

Packages

libraries in Java
collections of classes
java.lang 은 자동import됨

import java.text.NumberFormat
impott java.text.* // text 전부 import 

console input

import java.util.Scanner;

Scanner scannerObject = new Scanner(System.in);
Scanner scannerObj2 = new Scanner(System.in);
keyboard2.useDelimiter("##"); //scannerObj2에는 delimiter 부여, space는 delimiter 아님 

int n1; 
n1 = scannerObject.nextInt(); //21
double d1;
d1 = scannerObject.newDouble(); //2.1

String word1 = scannerObject.next(); //apple 
String line = scannerObject.nextLine(); // sentence

int numm = scannerObj.nextInt();
String junk = scannerObj.nextLine();
String s1 = scannerObj.nextLine();
String s2 = scannerObj.nextLine();
String 
String junk2 = scannerObj.nextLine();

String word1 = scannerObj2.next();
String word2 = scannerObj2.next();

//input: aa bb##cc dd##
//word1 : aa bb
//word2 : cc dd

in interactive program,
print prompt recommended before user input
& always echo all input!

Text File Input/Output

import java.util.Scanner; 
import java.io.FileInputStream;
import java.io.FileNotFoundException; 

public class TextFileDemo
{
	public static void main (String[] args)
    {
        Scanner fileIn = null; //initializes fileIn to empty
        try
        {
            //Attempt to open the file
            fileIn = new Scanner (
                new FileInputStream ("player.txt"));
         }
        catch (FileNotFoundException e)
        {
            //This block executed if the file is not found 
            //and then the program exits
            System.out.println("File not Found.");
            System.exit(0);
         }
        //if the program gets here than
        //the file was opened successfully
        int highscore; 
        String name;
        
        System.out.println("Text left to read?" + fileIn.hasNextLine());
        highscore = file.nextInt();
        fileIn.nextLine(); 
        name = fileIn.nextLine();
        
        System.out.println("Name:" + name);
        System.out.println("High score: " + highscore);
        System.out.println("Text left to read?" + fileIn.hasNextLine());
        fileIn.close(); 
        }
}

import java.io.PrintWriter;
import java.io.FileOutputStream; 
import java.io.FileNotFoundException; 

public class TextFileOutputDemo 
{
	public static void main (String[] args)
    {
    	PrintWriter outputStream = null; 
        try
        {
        	outputStream = 
            	new PrintWriter(new FileOutputStream("stuff.txt"));
        }
        catch (FileNotFoundException e)
        {
        	System.out.println("Error opening the file stuff.txt.");
            System.exit(0);
        }
        System.out.println("Writing to file");
        
        OutputStream.println("The quick brown fox");
        OutputStream.println("jumps over the lazy dog.");
        
        OutputStream.close();
        
        System.out.println("End of program");
    }
}

File <stuff.txt> after the program is run
The quick brown fox
jumps over the lazy dog.