[Java] make a list reading a txt file

// Java
// make a list reading a txt file

import java.io.*;
import java.util.*;

public class list_from_file_2 {

    public static void main(String[] args) throws IOException {
        
        Scanner scan = new Scanner(new File("list.txt"));
        List<String> doubles = new ArrayList<String>();
        
        while(scan.hasNext()){
            doubles.add(scan.next());
        }
        
        Collections.sort(doubles);
        for (String d : doubles) System.out.println(d);
        
        
    }
}
------------------------------------------------------------------------

// Java
// make a list reading a txt file

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class list_from_file {

    public static void main(String[] args) throws IOException {

        BufferedReader in = null;
        FileReader fr = null;
        List<String> list = new ArrayList<String>();   // String type data read from txt file

        try {
            fr = new FileReader("list.txt");
            in = new BufferedReader(fr);
            String str;
            while ((str = in.readLine()) != null) {
                list.add(str); // or list.setListData(str); // for jList
                //list.add(Double.parseDouble(str));  // if read data is double number
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            in.close();
            fr.close();
        }

        for (String d : list) System.out.println(d);
    }

}

[Java] array, for-each

// Java
// Array

class array
{
    public static void main(String[] args)
    {
        int[][] arr = new int[3][4];   // 2nd-order array
        for(int i=0; i<arr.length; i++)
            for(int j=0; j<arr[i].length; j++)
                arr[i][j] = i + j;
                
        for(int i=0; i<arr.length; i++)
        {
            for(int j=0; j<arr[i].length; j++)
                System.out.print(arr[i][j] + " ");
            System.out.println();
        }
        
        int [] ar = {1, 3, 5};  // 1st-order array => int[] ar = new int[] {1,3,5};
        for (int e : ar)    // for, each
            System.out.print(e + " ");
            
    }
}

[Java] file I/O

// Java
// text file read (line by line)
import java.io.*;
import java.util.*;   // to use "ArrayList"

public class file_IO_4 {
 
     public static void main(String[] args) {
           
            // File Open
            File oFile = new File("./animal/livestock.txt");
           
            // Creat object for File Reader
            FileReader frd = null;
            BufferedReader brd = null;
           
            // define "ArrayList" for saving line-by-line content of file 
            ArrayList<String> lineList = new ArrayList<String>();
 
            // variables for saving line by line
            String rLine = null;
            int lineNum = 0;
            boolean hasMore = true;
           
            try {
                  frd = new FileReader(oFile);
                  brd = new BufferedReader(frd);  
                                                         
                  System.out.println();
                  while (hasMore) {
                     if((rLine = brd.readLine())!= null){
                         System.out.println(rLine);
                               
                         // Add read line to ArrayList
                         lineList.add(rLine);
                         lineNum++;
                         hasMore = true;
                      } else
                         hasMore = false;                       
            }
                 
                  frd.close();
                  brd.close();
            } catch (IOException e) {
                  e.printStackTrace();
            }           
           
            // Print size of Array List 
            System.out.println();
            System.out.println(lineList.size());
            System.out.println(lineList);
            System.out.println();
           
            // Print line by line (for loop)
            lineNum = lineList.size();
            for(int i=0; i<lineNum; i++) {
             System.out.println( i +": "+lineList.get(i));
            }           
     }
}

---------------------------------------------------------------------

// Java
// file read and write

import java.io.*;   // to use file input/output
import java.util.*;  // to use Scanner (keyboard input)

class file_IO_2
{

    InputStreamReader isr = new InputStreamReader(System.in);
    BufferedWriter bw = null;
    BufferedReader br = null;
    
    Scanner scan = new Scanner (System.in);
    
    int menuNum;
    String input, output, filename = "sentences.txt";
    
    
    void p(Object ob) {
        System.out.print(ob);
    }
        
    
    public static void main(String[] args) throws Exception
    {
        file_IO_2  f2 = new file_IO_2();
        f2.menu();
    }
    
    
    void menu() throws Exception
    {
        p("\n");
        p("\t   1. Input sentences   \n");
        p("\t   2. Print sentences   \n");
        p("\t   3. Quit   \n");
        p("\n");
        p("\t   Select :  ");
        
        while(true) {
            if(scan.hasNextInt())  {
                menuNum = scan.nextInt();
                break;
            }  else  {
                p("Please enter number between 1 and 3   \n");
            }
            }
            
        switch(menuNum)  {
            case 1:
                input();
                break;
            case 2:
                output();
                break;
            case 3:
                break;
            default:
                p("Please enter number between 1 and 3   \n");
                menu();
        }
        
        isr.close();
        br.close();
        bw.close();
    }
    
    
    void input() throws Exception 
    {
        p("\nLet's start to input sentences   \n");
        p("If you want to stop, press \"Enter\" in an empty line   \n");
        
        bw = new BufferedWriter(new FileWriter(filename));
        br = new BufferedReader(isr);
        while(!(input = br.readLine()).equals(""))  {
            bw.write(input);
            bw.newLine();
        }
        
        p("File saved \n");
        
        bw.flush();
        menu();
    }
    
    void output() throws Exception
    {
        p("\nSentences in \"" + filename + "\" \n\n");
        br = new BufferedReader(new FileReader(filename));
        int lineCnt=0;
        while(true)  {
            lineCnt++;
            output = br.readLine();
            if (output == null) {
                break;
            }
            p(lineCnt + ". " + output + "\n");
        }
        menu();
    }
    
}

------------------------------------------------------------------------

// Java
// file read and write

// 1. input # of items
// 2. input item's name, price, location
// 3. write input data in a file "item.db"
// 4. read the file and print all items' name

import java.util.*;
import java.io.*;  // to use file input, also include "throws IOException" in main method declaration, or "throws Exception" to read file (object in the file)
import java.text.DecimalFormat;  // to use decimal format

class file_IO
{

 public static void main(String[] args) throws Exception
 {
        DecimalFormat df = new DecimalFormat ("#.##");
        
        String filename = "item.db";
        ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(filename));
        ObjectInputStream in = new ObjectInputStream(new FileInputStream(filename));
        
        // # of items
        System.out.println("total number of items");
        Scanner ni = new Scanner (System.in);    
        while(!ni.hasNextInt())
        {
            ni.next();  // if input is not integer value, ignore it.
            System.err.println("Input should be integer value");
        }
        int n = ni.nextInt();
        
        
        // keyboard input
        for (int nn=1; nn<=n; nn=nn+1)
        {
            System.out.println("Input name of item # " +nn);
            Scanner i1n = new Scanner (System.in);    
            String n1 = i1n.next();
        
            System.out.println("Input price of item # " +nn);
            Scanner i1p = new Scanner (System.in);    
            while(!i1p.hasNextDouble()) {
                i1p.next();  // if input is not integer value, ignore it.
                System.err.println("Input should be a number");  }
            double p1 = i1p.nextDouble();
            
            System.out.println("Input location of item # " +nn);
            Scanner i1l = new Scanner (System.in);    
            String l1 = i1l.next();

            Item i1 = new Item(n1, p1, l1);
            
            out.writeObject(i1);
        }
        out.close();
        
        System.out.println();
        
        
        Item read_object;
        while( (read_object = (Item) in.readObject()) != null)
        {
            System.out.println(read_object.getName());
        }
        in.close();
        
}
}
 
 
 class Item implements Serializable 
 {
    String name, location;
    Double price;
    
    public Item (String name, double price, String location)
    {
        this.name = name;
        this.price = price;
        this.location = location;
    }
    
    String getName()
    {
        return name;
    }
    
    double getPrice()
    {
        return price;
    }
    
    String getLocation()
    {
        return location;
    }
    
}

[Java] console output (println, print, printf)

\n  :  next line
\t  :  tab
\"  :  " (quotation mark)
\\  :  \ (backslash)

System.out.println("She said \"I love you.\" ");
     -->  She said "I love you."

System.out.print("I will");
System.out.print("get a job soon");
     -->  I will get a job soon


%d  :  Integer
%f  :  Real number
%e  :  Exponent
%c  :  Char
%s  :  String

System.out.printf("%d,  %f,  %e,  %c,  %s",  12, 3.44, 0.00223, 'S', "SHSJ");
     -->  12, 3.44, 2.23e-3,  S,  SHSJ

[Java] setText format (how to round number)

// Java
// how to round number


import java.text.DecimalFormat;

class round_number
{

 public static void main(String[] args)    // main method
 {
        
        DecimalFormat df = new DecimalFormat("#.##");
        
        double num = 3.141592;

        System.out.println(df.format(num));

 }
}

-----------------------------------------------------------------

in GUI (Netbeans),

import java.text.DecimalFormat;   // outside class

//inside method
DecimalFormat df = new DecimalFormat("#.##");
jLabel1.setText(df.format(num));

[Java] method with multiple instances (objects)

method_with_multiple_instances.java

// Java
// method with multiple instances (objects)

// works with NumberInput.java

class method_with_multiple_instances
{

 public static void main(String[] args)    // main method
 {
        NumberInput n1=new NumberInput();
        System.out.println("current value = " + n1.getNum());
        
        simpleMethod(n1);
        System.out.println("current value = " + n1.getNum());
}

    public static void simpleMethod(NumberInput calc1)
    {
        calc1.addNum(12);

    }
}

-------------------------------------------------------------------

NumberInput.java

// Java
// method with multiple instances (objects)

// works with method_with_multiple_instances.java

class NumberInput
{
    // instance (object) variable
    int result=0;
    
 public void addNum(int n1)     // method "addNum"
 {
 
        result = result + n1;
        
}

    public int getNum()
    {
        return result;
    }
}

[Java] method with reflection

// Java
// method with reflection


import java.util.*;

class method_with_reflection
{

// A java program must start with "main" method
 public static void main(String[] args)    // main method
 {
 
        System.out.println("first number for factorial?");
        Scanner scan1 = new Scanner (System.in);
        
        while(!scan1.hasNextDouble())
        {
            scan1.next();  // if input is not integer value, ignore it.
            System.err.println("Input should be number");
        }
        double n1=scan1.nextDouble(); 
        
        System.out.println("second number for factorial?");
        Scanner scan2 = new Scanner (System.in);
        
        while(!scan2.hasNextDouble())
        {
            scan2.next();  // if input is not integer value, ignore it.
            System.err.println("Input should be number");
        }
        double n2=scan2.nextDouble(); 

        if(n1==0 && n2==0) {
            bye();    // if weight was input 0, call method "bye"
            System.exit(0); }
                

        System.out.println();        
        System.out.println(n1 + " factorial = " + factorial(n1));  
        System.out.println(n2 + " factorial = " + factorial(n2)); 

}


 public static double factorial(double n)
 {
        if (n==1)
            return 1;
        else
            return n*factorial(n-1);
 }
 

 public static void bye()
 {
        System.out.println();        
        System.out.println("Good Bye");
 }
}

[Java] method with return values

// Java
// method with return values


import java.util.*;

class method_with_return
{

// A java program must start with "main" method
 public static void main(String[] args)    // main method
 {
 
        System.out.println("first number?");
        Scanner scan1 = new Scanner (System.in);
        
        while(!scan1.hasNextDouble())
        {
            scan1.next();  // if input is not integer value, ignore it.
            System.err.println("Input should be number");
        }
        double n1=scan1.nextDouble(); 
        
        System.out.println("second number?");
        Scanner scan2 = new Scanner (System.in);
        
        while(!scan2.hasNextDouble())
        {
            scan2.next();  // if input is not integer value, ignore it.
            System.err.println("Input should be number");
        }
        double n2=scan2.nextDouble(); 

        if(n1==0 && n2==0) {
            bye();    // if weight was input 0, call method "bye"
            System.exit(0); }
                
        
        System.out.println("What do you want?  (1) multiply, (2) divide");
        Scanner scan3 = new Scanner (System.in);
        
        while(!scan3.hasNextInt())
        {
            scan3.next();  // if input is not integer value, ignore it.
            System.err.println("Input should be 1 or 2");
        }
        int op=scan3.nextInt(); 


        if(op==1)
        {    System.out.println();        
            System.out.println(n1 + " * " + n2 + " = " + function1(n1, n2));  
        } else 
            {
                System.out.println();        
                System.out.println(n1 + " / " + n2 + " = " + function2(n1, n2));  
            }
}


 public static double function1(double n1, double n2)
 {
        return n1*n2;
 }
 
  public static double function2(double n1, double n2)
 {
        return n1/n2;
 }
 
 public static void bye()
 {
        System.out.println();        
        System.out.println("Good Bye");
 }
}

[Java] method without return value

// Java
// method


import java.util.*;

class method
{

// A java program starts with "main" method
 public static void main(String[] args)    // main method
 {
 
        System.out.println("What's your weight in kilogram?");
        Scanner scan1 = new Scanner (System.in);
        
        while(!scan1.hasNextDouble())
        {
            scan1.next();  // if input is not integer value, ignore it.
            System.err.println("Input should be number");
        }
        double weight=scan1.nextDouble(); 
        
        System.out.println("What's your height in centimeter?");
        Scanner scan2 = new Scanner (System.in);
        
        while(!scan2.hasNextDouble())
        {
            scan2.next();  // if input is not integer value, ignore it.
            System.err.println("Input should be number");
        }
        double height=scan2.nextDouble(); 

        if(weight==0) {
            bye();    // if weight was input 0, call method "bye"
            System.exit(0); }
                
        function1(weight, height);   // give "weight" and "height" values to method "fuction1"
        
}

 public static void function1(double weight, double height)
 {
        System.out.println();        
        System.out.println("Calories you daily need = "+(int)(weight*24));
        System.out.println();        
        System.out.println("Recommended weight for you = " + (int)(height-110) + " (female)");
        System.out.println("Recommended weight for you = " + (int)(height-100) + " (male)");        
 }
 
 public static void bye()
 {
        System.out.println();        
        System.out.println("Good Bye");
 }
}