Java Basic Rules
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// file name MyFirstClass.java
import java.util.*;
import java.lang.Math;
import java.io.*;
import javax.swing.*;
public class MyFirstClass{ // start of program
public static void main(String[] args) { // basic function main
// variables and calculation
int a=2;
int b=3;
int c=Integer.parseInt(JOptionPane.showInputDialog(" Put number: ", "1"));
System.out.println("Number is: "+c);
System.out.println(a+" * "+b+" = "+(a*b));
System.out.println("a^3 "+Math.pow(a,b));
//array
int[] array_my=new int[10];
array_my[0]=3;
array_my[1]=5;
System.out.println("Number of elements "+array_my.length+" 1 + 2 element of array "+(array_my[0]+array_my[1]));
//strings
String txt="Quick red fox";
String txt2=JOptionPane.showInputDialog("Write text: ", "word");
System.out.println("Text is: "+txt2);
String[] count_of_word=txt.split(" ");
System.out.println("Length: "+txt.length()+" Count of words "+count_of_word.length);
System.out.println(txt +" -> "+txt.replace("red","brown"));
System.out.println("First 5 chars of string is: "+ txt.substring(0,5));
//for a if
for(int i=0; i<10;i++){
if(i==3)System.out.println("i equal "+i);
}
// file
try {
File soubor=new File("some_file.txt");
if(!soubor.exists()){
System.out.println("File dont exist");
}
else { // utf-8 encoding
BufferedReader in1 = new BufferedReader(new InputStreamReader(new FileInputStream(soubor),"UTF-8"));
BufferedWriter out1 = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("zapis.txt"),"UTF-8"));
String str;
while ((str = in1.readLine())!=null){
System.out.println(str);
out1.write(str+"
");
}
in1.close();
out1.close();
}
} catch(IOException e){System.out.println("Error " + e);}
// dir
File pathName = new File("some_dir");
String[] fileNames = pathName.list();
if(pathName.exists())
System.out.println("Name of first file in \"some_dir\": "+fileNames[0]);
else System.out.println("dir not exist");
//function
int nResult = calculateMyFc(3,5);
System.out.println("Result of function: "+nResult);
} // end of function main
// new function , you can add to end MyFc = my function
public static int calculateMyFc(int a, int b){
return (a+b);
}
} // end of class of program
397LW NO topic_id
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Další témata ....(Topics)
Physical pixel (px)
Density independent pixel (dp)
Dots per inch (dpi) .. physical pixels per inch
px = dp * (dpi / 160)
Density independent pixel (dp)
Dots per inch (dpi) .. physical pixels per inch
px = dp * (dpi / 160)
public static int dpToPx(int dp)
{
return (int) (dp * Resources.getSystem().getDisplayMetrics().density);
}
public static int pxToDp(int px)
{
return (int) (px / Resources.getSystem().getDisplayMetrics().density);
}
if , else if, else statement with string as a switch statement in Java example source code.
MainClass.java
MainClass.java
public class MainClass {
public static void main(String[] arg) {
String[] arrayOfString = {"nothing", "Hello", "people"
, "bye-bye", "hello", "world!", "end" };
for (int i = 0; i < arrayOfString.length; i++) {
if (arrayOfString[i].equals("Hello"))
System.out.println(arrayOfString[i]);
else if (arrayOfString[i].equals("people"))
System.out.println(arrayOfString[i]);
else if (arrayOfString[i].equals("hello"))
System.out.println(arrayOfString[i]);
else if (arrayOfString[i].equals("world!"))
System.out.println(arrayOfString[i]);
else // default
System.out.println("Default");
}
}
}
/*
Default
Hello
people
Default
hello
world!
Default
*/
Foreach in Java basic example source code.
MainClass.java
MainClass.java
public class MainClass {
public static void main(String[] arg) {
String[] arrayOfString = { "Hello", "people", "hello", "world!" };
for (String s : arrayOfString)
System.out.println(s);
}
}
Basic difference remember it!!!
if(TRUE && TRUE && TRUE) return TRUE otherwise FALSE
if(FALSE || FALSE || FALSE) return FALSE otherwise TRUE
Logical operator and &&
If all conditions/operands is TRUE return TRUE, otherwise return FALSE
Logical operator or ||
The logical OR operator (||) returns the boolean value true if either or both operands is true and returns false otherwise.
If one operands is TRUE, condition is TRUE:
rev
if(TRUE && TRUE && TRUE) return TRUE otherwise FALSE
if(FALSE || FALSE || FALSE) return FALSE otherwise TRUE
Logical operator and &&
If all conditions/operands is TRUE return TRUE, otherwise return FALSE
if( true and true and true){
// return true - do something
}
int a = 6;
if(a == 6 && a == 6 ) {
// if TRUE
// true && true return true, do something
}
if(a == 6 && a == 5){
// nothing, not attended
}else{
// true && false return false, or false && false return false
// do something
}
Logical operator or ||
The logical OR operator (||) returns the boolean value true if either or both operands is true and returns false otherwise.
If one operands is TRUE, condition is TRUE:
if(FALSE OR FALSE OR TRUE) return TRUE
if(FALSE OR TRUE OR FALSE) return TRUE
if(FALSE OR FALSE OR FALSE) return FALSE
int a = 6;
if(a==6 || a==5){ // TRUE || FALSE return TRUE
//if return TRUE
//one from operadns is TRUE return true, do something
}
if(a==5 || a==4){ // FALSE || FALSE return FALSE
// not attended
}else{
//if return FALSE, do something
}
rev
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(new SampleView(this));
}
private static class SampleView extends View {
// CONSTRUCTOR
public SampleView(Context context) {
super(context);
setFocusable(true);
}
@Override
protected void onDraw(Canvas canvas) {
//drawARGB (int a, int r, int g, int b)
// a alpha component (0..255) of the color to draw onto the canvas
// r red component (0..255)
// g green component (0..255)
// b blue component (0..255)
canvas.drawARGB(255, 0, 255, 10);
}
}
}
Editace: 2013-12-09 11:06:19
Počet článků v kategorii: 397
Url:java-basic-rules
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