Opening Prayer Programs

To compare strings, you should use (or rather what should be) using the equals method, but you may never have used an expression like this:

 
 public static void main ( String [] args) {String 
 = "Hello"; 
 if ("". Equals (a)) 
 {System.out.println ("String is empty"); 
}} 
 
 

Actually not very funny we're just calling the equals method of the String class, a String that is quoting but it has some advantages, such as creating an if to validate that user input is empty, but where is the advantage?.

Well if we have a String to and want to see it empty, the comparison would be very simple:

 
 if (a.equals ("") {
 System.out.println ("String is empty");} 
 
 

But we must also validate that the String is not null, because if for example we are recovering in a Servlet, if the parameter was not sent, the String is null, then our comparison should look like:

 
 if (to! = null & & a.equals 
 ("")) {System.out.println ("String is empty");} 
 
 With 

This last amendment, we will assume that the compiler is able to recognize that if the first condition is met, will not run no more and not throw an exception, but since that would take something (in fact they do well), the comparison should be something like:

 public static void main (String [] args) {
 String a = "Hello"; 
 if (to! = null) {
 if (a.equals ( ") 
 {System.out.println (" String is empty "); 
 
}}} 
 
 
 

However this problem can be solved easily as follows:

 public static void main (String [] args) 
 {String a = null; 
 if ("". equals (a)) 
 {System.out.println ("String is empty"); 
}} 
 

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Comparing Strings Array Copy

arrangements are an important way to save data. If we have to make a copy of arrangements we can make it in this way.

 public class Copy () {
 int [] array = new int [55555]; 
 
 
} public int [] copyArray () {
 int [] arraycopy = new int [Array.length] 
 for (int i = 0; i \u0026lt;Array.length; i + +) 
 arraycopy [i] = array [i]; 
 arraycopy return;} 
 

For each position we copy the value of an array to another, this is a way but there is a better and easier. For this review the documentation (API documentation ) Exists in the class System a method called arraycopy.

arraycopy public static native void (Object src, int srcPos, Object dest, int destPos, int length)

This method is native, so the copy will be made in memory segment making it faster. This method gives us the ability to copy also segments of the original arrangement.

 System.arraycopy (array, 5, array, 0, Array.length-5); 

Copying from the 5-position under

Bibliography:

Dactonta, Michael C. Monk, Eric, Keller Paul, Java Pitfalls, Wiley 2000;

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Create a timer

Java is one of the most widely used programming languages \u200b\u200bor at least the most famous. One weakness is the speed of implementation (which has been improved) and RAM memory consumption,

order to perform the famous "benchmarks" that can measure the execution time , this can be done through a class that simulates a stopwatch.

 
 public class Stopwatch {private long startTime = -1; 
 stopTime private long = -1; 
 private boolean running  = false; 
    
   public Stopwatch start(){ 
      startTime = System.currentTimeMillis(); 
      running = true; 
      return this; 
   } 
    
   public Stopwatch stop(){ 
      stopTime = System.currentTimeMillis(); 
      running = false; 
      return this; 
   } 
    
   public Stopwatch reset(){ 
      startTime = -1; 
      stopTime = -1; 
      running = false; 
      return this; 
   } 
    
   public long getElapsedTime(){ 
      if(startTime == -1) 
        return 0; 
      else if(running) 
        return System.currentTimeMillis() - startTime; Else return 
 
 stopTime - startTime; 
}} 
 

To use this class we just have to instantiate and call the necessary methods.

Example:

 public static void main (String [] args) {
 Stopwatch timer = new Stopwatch (). Start (); 
 long total = 0; 
 for (int i = 0; i Integer.MAX_VALUE; i + +) {
 total + = i;} 
 
 System.out.println (timer.getElapsedTime ());} 
 

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Hi, I'm Zabdiel

Hi all, the reason for this post is to introduce myself, I am Zabdiel student ITC (Computer Engineering Technology) study my the 8th semester.

The purpose of this blog is the power to tutorials and tips to help allgunos same problems we've had and we would have liked to have a place to look for how to solve them. So we welcome your comments and questions.

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java parameter passing: by value

parameters by value.

is used when required to pass the value of a variable to a function and that is performing some operation on this value, function or method creates a local variable and worked on it.

int a = 5;

method (a):

void method (int c) {System.out.println

(c);}

The variable c is a local variable that receives a copy of the value of the variable, ie the parameter is passed by value.

Step by reference.

Passing by reference instead of sending the value of the variable, it sends the memory address which is stored in this way to modify the contents of the variable. However, this type of passing parameters in Java does not exist but if you would like to do in C + + look like this:

include

using namespace std;

void function (int & a) {

a = 10;

}

int main () {int

var = 5;

function (& var);

court

<<>

}

The outturn would be 10 and the variable 10 is passed by reference, the function modifies its value.

Now back to the important parameters How does Java? In java there is only one way to do it and over PARAMETER worth, here 's an example of this:

PasoPorValor {public class

public static void main (String [] args) {

int a = 20;

method (a);

System.out.println (a);

}

public static void method (int c) {

c = 10;

}

}

The value of the variable is always the same. Now an example using objects, in this case will use an array, since by definition arrays are objects:

PasoPorValor {public class

public static void main (String [] args) {

int [] a = new int [1] / / declare an array of position;

method (a);

System.out.println (a [0]);

}

public static void method (int [] c) {

c [0] = 10;}

}

But it happened! Why the value changed my order? In fact this happens for the simple reason that Java variables pointing to objects, not the object but a reference to it, ie when we do this in Java:

int [] a = new int [1];

We are creating a reference to and that's how to handle the data type referenced is an array of int and also right there with the new operator is created object, and therefore the variable will refer to the memory location of that object.

So when the method receives a reference and adjust, we are modifying the value of the object, but beware, this does not mean that Java passes parameters by reference, it passes the value of

REFERENCE

If Java pass by reference values \u200b\u200bwhen we do this:

PasoPorValor {public class

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

a = "Hello";

method (a) ;

System.out.println (a);

}

public static void method (String c) {

c = "New Object";}

}

The result should be "New Object" However this does not happen for the simple reason that Java passes parameters by value only

hope with this is a bit more clear how it happens Java parameters

Greetings

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Hello, my name is Gustavo!

Hello, my name is Gustavo Villegas, I have 19 years almost 20, he studied Computer Engineering Technology in Motnerrey Tech 5th semester just finished and pss I think you can say I'm in 6th. I like computers, programming, I think I'm a little Geek, but not much light haha. In addition to that I also like cars, including "American muscle." It used to be a little more fan of video games, but the truth is that lately I've lost the taste and all the time, besides not having money for a PS 3: (

Well I'll be posting here every as possible, to give an occasional tip of a software news etc ... and be given such information, tips or tutorials that usually occurs in a Blog. In particular the area that interests me now is the Web programming, but I also like other things in programming in general. I program in Java (that is what we say that somehow I am less ignorant lol) also I have some other bits of knowledge but very little in PHP, ASP.NET, ASP (The old), C #, C + +, C and "HASKELL". And I know some things are known standard for web, HTML, JavaScript, XML, JSON etc ...

I will be writing this blog along with my classmates (so far) Zab (8th) and Ger (6th, my generation) and pss I hope will be helpful. If you have any questions I will gladly send you an email and if I can help I will gladly. And since in truth, I do not think many people read this, but if one day this blog grows and I hope you read more visits hahaha.

Gus

Greetings!