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Tag: cat

Example of Unix commands implemented in Java

I created some illustrative and simple implementations of common Unix commands. For those who are familiar with Unix-like systems them make easier to understand Java. For those who are familiar with Java them make easier to understand Unix-like systems. :-)

1. PWD

The first one is pwd that show the current working directory.

public class Jpwd {
    public static void main(String[] args) {
        String pwd = System.getProperty("user.dir");
        System.out.println(pwd);
    }
}

Running this at /home/silveira directory gives us as output:

$ java Jpwd

/home/silveira

1. CAT

The command cat is usually utilized for displaying files.

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
 
public class Jcat {
    public static void main(String[] args) {
        if(args.length==1){
            try {
                FileReader fileReader = new FileReader(args[0]);
                BufferedReader in = new BufferedReader(fileReader);
                String line;
                while((line = in.readLine())!= null){
                    System.out.println(line);
                }
            } catch (FileNotFoundException ex) {
                System.out.println(args[0]+", file not found.");
            }
            catch (IOException ex) {
                System.out.println(args[0]+", input/output error.");
            }
        }
    }
}

$ java Jcat /etc/timezone

America/Fortaleza

3. LS

The command ls is to list files. The File API (java.io.File) is very flexible and portable, but in this example I want just list files and directories of the current directory.

import java.io.File;
 
public class Jls {
    public static void main(String[] args) {
        File dir = new File(System.getProperty("user.dir"));
        String childs[] = dir.list();
        for(String child: childs){
            System.out.println(child);
        }
    }
}

Usage:

$ java Jpwd

/home/silveira/example

$ java Jls

directoryA

fileA

.somefile

4. CD

The cd command changes the current working directory.

import java.io.File;
 
public class Jcd {
    public static void main(String[] args) {
        if(args.length==1){
            File dir = new File(args[0]);
            if(dir.isDirectory()==true) {
                System.setProperty("user.dir", dir.getAbsolutePath());
            } else {
                System.out.println(args[0] + "is not a directory.");
            }
        }
    }
}

Usage:

$ java Jpwd
/home/silveira
$ java Jcd /tmp
$ java Jpwd
/tmp

Gato em JavaFX, versão 2

Lembra daquele nosso gato em Java FX? Agora ele move os olhos com cliques em botões.



Código fonte:

import javafx.ui.canvas.*;
import javafx.ui.*;
 
class Cat extends CompositeNode{
    attribute look: Number; // -1.0 to 1.0
    operation lookLeft();
    operation lookCenter();
    operation lookRight();
}
 
attribute Cat.look = 0; // 0 = middle
 
operation Cat.lookLeft(){
    look = [look, look - 0.1 .. -1.0] dur 1000;
}
 
operation Cat.lookCenter(){
    var step = if look < 0 then 0.1 else -0.1;
    look = [look, look+step .. 0.0] dur 1000;
}
 
operation Cat.lookRight(){
    look = [look, look + 0.1 .. 1.0] dur 1000;
}
 
function Cat.composeNode(){
    var head =  Ellipse {cx:100, cy:100, radiusX:100, radiusY:50, fill:black };
    var rightEar =  Arc {x:100, y:10, height:150, width:100,
                       startAngle:-20, length:90, closure:PIE, fill:black};
    var leftEar = Arc {x:000, y:10, height:150, width:100,
                     startAngle:110, length:90, closure:PIE, fill:black};
    var leftEye = Ellipse { cx:60, cy:100, radiusX:30, radiusY:15, fill:white};
    var rightEye = Ellipse { cx:140, cy:100, radiusX:30, radiusY:15, fill:white};
    var nose = Arc { x:85, y:110, height:20, width:30,
                     startAngle:45, length:90, closure:PIE, fill:white};
 
    var rightIris = Ellipse { cx: bind 140+look*20, cy:100,
                     radiusX:5, radiusY:15, fill:black};
    var leftIris = Ellipse { cx: bind 60+look*20, cy:100,
                     radiusX:5, radiusY:15, fill:black};    
 
    return Group{content: [head, rightEar, leftEar, leftEye,
                     leftIris, rightEye, rightIris, nose]};
}
 
var myCat = Cat{};
 
var myCatControl = View {
            transform: [translate(0, 150)]
            content: GroupPanel {
                cursor: DEFAULT
                var row = Row {alignment: BASELINE}
                var column1 = Column { }
                var column2 = Column { }
                var column3 = Column { }
                var column4 = Column { }
                var column5 = Column { }
                rows: [row]
                columns: [column1, column2, column3, column4]
                content:
                [SimpleLabel {
                    row: row
                    column: column1
                    text: "Look:"
                },
                Button {
                    row: row
                    column: column2
                    mnemonic: L
                    text: "Left"
                    action: operation() {
                        myCat.lookLeft();
                    }
                },
                Button {
                    row: row
                    column: column3
                    mnemonic: C
                    text: "Center"
                    action: operation() {
                        myCat.lookCenter();
                    }
                },
                Button {
                    row: row
                    column: column4
                    mnemonic: R
                    text: "Right"
                    action: operation() {
                        myCat.lookRight();
                    }
                }]
                }
            };
 
Canvas {
    content: [myCatControl, myCat]
}

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