Declaring String object

Is it a good practice to initialize a String object variable to a zero length string?
String strMyString = "";and later, when we need to assign a new value for it, we just do
strMyString = "Hello World";This is correct or not?

It's only appropriate if you want an empty string to be the default, and you don't invariably reassign it. This doesn't happen very often; usually you either can (and should) unambiguously find a value for it, or you can just use null, or you don't need a default at all.

Similar Messages

Declaring String type and instantiating object

I am using this JavaBean but I think I shouldnt be declaring String type with emply values and also instantiating the bean in the no arg constructor with null values:
public class SimpleBean {
     private String firstname = "";
                private String lastname = "";
     public SimpleBean()
                      firstname = null;
                      lastname = null;
..Please advise.

Evergrean wrote:
Thanks,
Instead of setting them to null in the Constructor I assume I should have nothing in it?Right. In fact, if that's the only constructor, and you don't do anything else in it, you can dispense with it entirely. If you don't write any constructors, the compiler will generate one for you: a default constructor that takes no arguments and does nothing but call super().

String Object info not getting displayed in outgoing referrences .

Hi,
Iam new to MAT and is in learning stage.
Iam having a sample java program , whch has got String objects printed contunously . In order to take the heap dump while running itself , I am running this application for 2 minutes and in between Im taking the heap dump , but when analysed my java class , found that there is no entry for String objects under outgoing referrences of the java class from histogram.
Please help me to find out why String object details are not present in outgoiing referrences for the java class.
My Java Program,
public class B{
public static void main(String[] args) {
          //create Calendar instance
         Calendar now = Calendar.getInstance();
         System.out.println("Current time : "+ now.get(Calendar.HOUR_OF_DAY)+ ":" + now.get(Calendar.MINUTE)+ ":"+ now.get(Calendar.SECOND));
         int m = now.get(Calendar.MINUTE);
         B b = new B();
         b.print();
public void print( int m2, Calendar now2){
           while ( (m2+2) >= now2.get(Calendar.MINUTE)){
                   String x = "xxxxxx";
                    System.out.println("String"+x);

Hi,
Do you mean this String object?
   String x = "xxxxxx";
If so, then here the explanation. The String above is declared as a loca variable in the print method. I can't see any field pointing to it (neider an object insance is pointing to it, nor a static reference from the class).
This local object will be in the heap as long as the method is running, and in the heap dump you will see such objects marked as GC roots. The type of this GC root will be <Java local> .
Depending on the heap dump format, there may be also stack traces inside. If there are stack traces, you shold be able to see your object as referenced from the corresponding frame (the print method) in the Thread Stacks query.
I hope this helps.
Krum

Strange about invoking web service method declared string method(void);

Dear forum readers
Im experimenting with OpenESB and web services. Ive create a simple web service using NetBeans 6.1. The method consists of a single method, getTime, that is declared:
String getTime()
My current experiment is to invoke this method from a BPEL-process using the Invoke process object. The strange thing is that it seems like I have to provide a dummy inbound variable from the BPEL-designer even though the method doesnt take any parameters. I include a snippet from the BPEL process below which includes the section where I set the dummy GetTimeIn-variable and then invokes the WS method getTime().
<assign name="Assign2">
<copy>
<from>'DummyValue'</from>
<to variable="GetTimeIn" part="parameters"/>
</copy>
</assign>
<invoke name="Invoke1" partnerLink="PartnerLink1" operation="getTime" xmlns:tns="http://ws/" portType="tns:MyWebService" outputVariable="GetTimeOut" inputVariable="GetTimeIn"/>
If I dont initiate the dummy variable or remove it altogether, I cant successfully call the method. If I include the dummy in-parameter the call works just fine and I get back the current time as a string.
I must admit that Im still a rookie to web services, especially when calling them from a BPEL-process, so it may be a very trivial reason for this behaviour. Anyway, any help on this matter would be greatly appreciated.
Regards, Ola

Thank you both for the response. Regarding Rennays posting I have an additional question. When I create a new web service I don't have the "Document Literal" option nor a "Concrete Configuration" tab. I've created the web service using the "Web Application" project type and then adding a web service using the "Web Service..." wizard. This wizard doesn't have the configuration properties you mention, but if I add a WSDL-file to a BPEL-project the wizard has the properties you mention.
Is it possible to create a web service, programmed as an ordinary Java-class, from an existing WSDL-file? In that case it may solve the problem with the Document Literal property. Currently I dont know any other way to create such a web-service other than the through the web service wizard in a web application project. Of course, its possible to craft it from scratch but thats to much work to be practical.
Regards, Ola

XML validation with DTD stored in String object

Does anyone know if this is plausible......
I am trying to validate some XML with a DTD... easy enough, right? The catch is that the dtd is NOT stored in a file somewhere and is also not declared in the XML to be validated. It is stored in a String object (as is the XML file to be validated).
To clarify - I want to do something like this... but not sure how to incorporate the DTD.
String dtd = // dtd definition here
String xml = // xml text here (no URI at the top)
SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser parser = factory.newSAXParser();
DefaultHandler handler = new DefaultHandler(); // DTD handler??
parser.parse(new InputSource(new StringReader(xml.toString())), handler);any help would be greatly appreciated.
thanks in advance,
Terrance

I guess it makes the most sense to make the dtd local to the xml. Therefore I would only have one string with both the xml contents and dtd contents. That is how I am going to approach this unless I hear something different.

So how do you declare an object?

Okay I have a program I'm trying to build that lets me navigate between menus...
Main Menu starts up:
(Unimportant)
Then it takes me to another Menu.
When this is over I want to go back:
   System.out.println("Select: ");
        System.out.println("1: to Return to the main menu");
        System.out.println("or");
        System.out.println("0 to Exit");
     if(input.nextInt()==1){
         main(); // <-- error here
     else if(input.nextInt()==0){
         System.exit(0);
        }   It doesnt find the main method because I didn't declare it as an object at the top...
How do I do that?
Edited by: tark_theshark on Mar 30, 2008 5:24 AM

Nah, this has nothing to do with declaring an object, and you really don't want to do this. What you really want to do is to have a loop of some kind, say a while loop and have the loop repeat until the user presses "0". Something like so:
    public static void main(String[] args)
        boolean done = false;
        while (!done)
            if(input.nextInt() == 0)
                done = true;
    }Edited by: Encephalopathic on Mar 30, 2008 6:27 AM

Help needed to understand String object

Hi all,
I want to understand the difference in statements
new String("") and string declared as "".
Is this only a shortcut or is there any other difference like re-using the string objects created in the pool?
what is the value in the String instantiated as new String()
Thanx

Hi all,
I want to understand the difference in statements
new String("") and string declared as "".
Is this only a shortcut or is there any other
difference like re-using the string objects created in
the pool?
what is the value in the String instantiated as new
String()
ThanxLiteral strings are internalized and reused, whereas new String always creates a new object.
Thus
String s = "";
is better than
String s = new String("");
The purpose of the String copy constructor is not made explicit in the API docs, but if you look at Sun's code, you will see that it can serve a purpose:
Substrings reference the same underlying char array as the String they are a substring of - they just have a different offset into that array, and a different length. The copy constructor however, creates a String with a new underlying char array, that contains only the relevant 'subarray' of the original String' sunderlying char array. So, if your code receives a large String, and then discards that String and passes around a substring of it, you might find you save a great deal of memory by using new String(s.substring(x, y));
Note however that these comments are based solely on Sun's core API code, and it might not be the case that other vendors implement String the same way, or that Sun will continue to do so into the future.

How many string objects - please suggest

Hi there,
Can you somebody please tell how many String objects will be created when the following method is invoked?
public String makinStrings() {
String s = Fred;
s = s + 47;
s = s.substring(2, 5);
s = s.toUpperCase();
return s.toString();
Thanks
Shan

Hi VShan,
This is your code
public String makinStrings() {
String s = Fred;     //1
s = s + 47;            //2
s = s.substring(2, 5);//3
s = s.toUpperCase(); //4
return s.toString();     //5
EXPLANATION : String is an immutable object, that means the String object cannot change it's contents.It might sound very unfamiliar but it is TRUE. In line 1: You declare a String object by assigning a a String literal "Fred" to the variable s. Now when you concat "47" with the original contents of s , a new memory space is allocated where s is assigned.+It is important to note+ that the previous reference of s i.e. "Fred" will be lost and now s refers to a new memory location where the contents are "Fred47" , so you have created another object in Line 2. Similarly you create another object in line3 & 4.As far my calculations you have created 4 objects.
I would like you to kindly note that s is already a String so you can directly return s and hence there is no need of s.toString() in Line 5.You should also note that each object is also an eligible candidate for Grabage Collection.
So as soon as Line2 gets executed , the object in Line1 becomes eligible for garbage collection.. that means when GC runs that object will be reclaimed and hence memory will be freed.

Error accesing/using a String object.......

Hi again folks!
Well now I have other problem, I don?t know what's happening, but I have simple C++ program as shared object which retrieves information from a Database, with the query results it makes a single string with all the data retrieved.
This C++ program is called by a Java program using JNI, but when my Java program receives the string and tries to parse it with the StringTokenizer object I get an error like this:
SIGSEGV 11* segmentation violation
si_signo [11]: SIGSEGV 11* segmentation violation
si_errno [0]: Error 0
si_code [1]: SEGV_ACCERR [addr: 0x45cb2448]
stackbase=DFFFF0A0, stackpointer=DFFFD0CC
Full thread dump:
"SIGQUIT handler" (TID:0xdd300190, sys_thread_t:0x42020, state:R, thread_t:
t@5, sp:0x0 threadID:0xdeaf0dd8, stack_base:0xdeaf0d6c, stack_size:0x20000) prio
=0
"Finalizer thread" (TID:0xdd3000d0, sys_thread_t:0x41fb8, state:CW, thread_t
: t@4, sp:0x0 threadID:0xdebb0dd8, stack_base:0xdebb0d6c, stack_size:0x20000) pr
io=1
"main" (TID:0xdd3000a8, sys_thread_t:0x42908, state:R, thread_t: t@1, sp:0x0
threadID:0x20a18, stack_base:0xdffff0a0, stack_size:0x800000) prio=5 *current t
hread*
ObjectFactory.createObject(Compiled Code)
Test.main(Compiled Code)
Registered Monitor Dump:
PCMap lock: <unowned>
Thread queue lock: <unowned>
Name and type hash table lock: <unowned>
String intern lock: <unowned>
JNI pinning lock: <unowned>
JNI global reference lock: <unowned>
BinClass lock: <unowned>
Class loading lock: owner "main" (0x42908, 1 entry)
Java stack lock: <unowned>
Code rewrite lock: <unowned>
Heap lock: <unowned>
Has finalization queue lock: <unowned>
Finalize me queue lock: <unowned>
Waiting to be notified:
"Finalizer thread"
Monitor cache expansion lock: <unowned>
Monitor registry: owner "main" (0x42908, 1 entry)
Abort (core dumped)
I dont know if I have to do something special before use the String, what's happening?
Any comment will be welcome.
Thanks in advance.

I hope this could help to clarify the scenario
In a previous query I get the number of rows returned by the next query
this number is stored at SQL_NUM_SEGS.arr variable. When I have the number of rows I reserve memory for the char array that I'm going to return with all the information.
AC01_TRAMA=(char *)malloc(atol(SQL_NUM_SEGS.arr) * INT02_TAM_SEG);
/*embedded PL/SQL code*/
EXEC SQL DECLARE CUR_EMISORA CURSOR FOR
SELECT rtrim(to_char(NUM_EMISORA)) || '|' || rtrim(SERIE) || '|' || EMISORA || '|' || STATUS FROM NUCL_EMISORA WHERE STATUS NOT LIKE 'BAJA';
EXEC SQL OPEN CUR_EMISORA;
The next lines of code generate a string like this:
"UTIL0000|366|239|93-1|FINASA |VIGE|243|3-90|BONSER |VIGE|248|2-94|BONSER |VIGE|287|970403|GOBFED |VIGE|362|93-4|BANOBRA |VIGE|404|2-90|BONSER |VIGE|407|2-95|FINASA |VIGE|633|95|BANMEXI |VIGE|641|2-94|PROMEX |VIGE|645|1-95|FINASA |VIGE|647|1-96|FINASA |VIGE|660|92|BANORTE |VIGE|677|93-3|BANOBRA |VIGE|678|1-90|BIATLAN |VIGE|736|2-95|BONSER |VIGE|786|1-94|BNCI |VIGE|1007|021024|GOBFED |VIGE|1008|021121|GOBFED |VIGE|"
this string is assigned to AC01_TRAMA(char pointer)and then I return this string in the next way:
return ( (env)->NewStringUTF(AC01_TRAMA) );
My java program is this:
public class Monitor
public native String consultaGeneral();
static
System.load("/afs/invermexico.com.mx/usr2/salponce/gustavo/jni/src_db/Monitor.so");
public String getTrama()
     String strTrama=consultaGeneral();
return strTrama;
public static void main(String []args)
String strEmisora, strNumEmisora, strStatus,strSerie;
Monitor m=new Monitor();
System.out.println(m.getTrama());
/*java.util.StringTokenizer STk = new java.util.StringTokenizer(m.getTrama(),"|");
while(objSTk.hasMoreTokens())
strEmisora = objSTk.nextToken();
strNumEmisora = objSTk.nextToken();
strStatus = objSTk.nextToken();
strSerie = objSTk.nextToken();
System.out.println("\n<------>\n"+ strEmisora+"\n"+strNumEmisora+"\n"+strStatus+"\n"+strSerie);
}//while
Well, this java program works fine but if I try to create an String tokenizer with it the program crashes, even if I assign the result into a new String object.
I'm going to put all the code rigth here
C++ program
#include "ast_bd.h"
#include "Monitor.h"
#include <stdlib.h>
#include <stdio.h>
#include <strings.h>
#include <jni.h>
#define CHA01_NOMBRE_APP "UTIL0000"
#define CHA02_FIN_DE_SEG "|"
#define INT01_TAM_LONG 20
#define INT02_TAM_SEG 52 /*52 BYTES; Tama�o de los 4 datos en conjunto*/
Prop�sito :-Determinar cuales son las emisoras con estado de vigente
o bloqueado.
-Obtener los datos de una emisora espec�fica.
-Actualizar los datos de una emisora espec�fica.
JNIEXPORT jstring JNICALL Java_Monitor_consultaGeneral
(JNIEnv *env, jobject obj)
long LO01_STATUS=1;
char CH01_NUM_SEGS[INT01_TAM_LONG];
char AC01_TRAMA, AC02_SEG;
EXEC SQL BEGIN DECLARE SECTION;
VARCHAR SQL_NUM_SEGS[INT01_TAM_LONG],
SQL_RESULT[INT02_TAM_SEG];
EXEC SQL END DECLARE SECTION;
EXEC SQL WHENEVER SQLERROR CONTINUE;
open_db();
EXEC SQL SELECT to_char(COUNT(1)) INTO:SQL_NUM_SEGS FROM NUCL_EMISORA WHERE STATUS NOT LIKE 'BAJA';
LO01_STATUS = sqlca.sqlcode;
if( !LO01_STATUS ) /*si todo sali� bien*/
strcpy(CH01_NUM_SEGS,SQL_NUM_SEGS.arr);
CH01_NUM_SEGS[SQL_NUM_SEGS.len]='\0';
AC01_TRAMA=(char *)malloc(atol(SQL_NUM_SEGS.arr) * INT02_TAM_SEG);
sprintf(AC01_TRAMA,"%s|%s|\0", CHA01_NOMBRE_APP, CH01_NUM_SEGS);
EXEC SQL DECLARE CUR_EMISORA CURSOR FOR
SELECT rtrim(to_char(NUM_EMISORA)) || '|' || rtrim(SERIE) || '|' || EMISORA || '|' || STATUS FROM NUCL_EMISORA WHERE STATUS NOT LIKE 'BAJA';
EXEC SQL OPEN CUR_EMISORA;
LO01_STATUS = sqlca.sqlcode;
if( !LO01_STATUS ) /*si todo sali� bien*/
do
EXEC SQL FETCH CUR_EMISORA INTO :SQL_RESULT;
LO01_STATUS = sqlca.sqlcode;/*Recuperamos el estado de la operacion fetch*/
if( !LO01_STATUS )
AC02_SEG=(char *)malloc(SQL_RESULT.len);
strcpy(AC02_SEG,SQL_RESULT.arr);
AC02_SEG[SQL_RESULT.len]='\0';
strcat(AC01_TRAMA,AC02_SEG);
strcat(AC01_TRAMA,CHA02_FIN_DE_SEG);
}/*if fetch correcto*/
else
LO01_STATUS=1;
}while(!LO01_STATUS);
EXEC SQL CLOSE CUR_EMISORA;/*Cerramos el cursor*/
Si no se recuperaron registros, se indicara en el numero de segmentos
al inicio de la trama.
}/*if open cursor*/
}/*if conteo*/
puts(AC01_TRAMA);
return ( (env)->NewStringUTF(AC01_TRAMA) );
}/*consulta_general*/
Java programs
public class Monitor
public native String consultaGeneral();
static
System.load("/afs/invermexico.com.mx/usr2/salponce/gustavo/jni/src_db/Monitor.so");
public String getTrama()
     String strTrama=consultaGeneral();
return strTrama;
public static void main(String []args)
String strEmisora, strNumEmisora, strStatus,strSerie;
Monitor m=new Monitor();
System.out.println(m.getTrama());
/*java.util.StringTokenizer STk = new java.util.StringTokenizer(m.getTrama(),"|");
while(objSTk.hasMoreTokens())
strEmisora = objSTk.nextToken();
strNumEmisora = objSTk.nextToken();
strStatus = objSTk.nextToken();
strSerie = objSTk.nextToken();
System.out.println("\n<------>\n"+ strEmisora+"\n"+strNumEmisora+"\n"+strStatus+"\n"+strSerie);
}//while
Thank's

How do I read two dimentional string object in C through JNI

HI,
I am new to JNI and Java as well. I want to read two dimentional string object passed by java to a native method written in C/C++. Say for example I have declared a two dimentional string object as below:
In Java
class InstanceFieldAccess {
private String [][] originalAddress = new String[][13];
private static native String [] accessField(String [][] referenceAddress);
public static void main(String args[]) {
/// Java code to get the string object and pass the string object to native method
new InstanceFieldAccess ().accessField(referenceAddress);
static {
System.loadLibrary("ReadStr");
In C/C++
I want to read the passed two dimentional string array in C/C++ native code and do the further processing and pass the string
back to Java class.
Could anybody tell me how to write the corresponding C/C++ native method.
Thanks in Advance.
Pramod.

i got it thanks.

Can we change data in string object.

Can we change data in string object.

Saw this hack to access the char[]'s in a String in another thread. Beware that the effects of doing this is possible errors, like incorrect hashCode etc.
import java.lang.reflect.*;
public class SharedString {
        public static Constructor stringWrap = null;
        public static String wrap(char[] value, int offset, int length) {
                try {
                        if (stringWrap == null) {
                                stringWrap = String.class.getDeclaredConstructor(new Class[] { Integer.TYPE, Integer.TYPE, char[].class });
                                stringWrap.setAccessible(true);
                        return (String)stringWrap.newInstance(new Object[] { new Integer(offset), new Integer(length), value });
                catch (java.lang.NoSuchMethodException e) {
                        System.err.println ("NoMethod exception caught: " + e);
                catch (java.lang.IllegalAccessException e) {
                        System.err.println ("Access exception caught: " + e);
                catch (java.lang.InstantiationException e) {
                        System.err.println ("Instantiation exception caught: " + e);
                catch (java.lang.reflect.InvocationTargetException e) {
                        System.err.println ("Invocation exception caught: " + e);
                return null;
        public static void main(String[] args) {
                char[] chars = new char[] { 'l', 'e', 'v', 'i', '_', 'h' };
                String test = SharedString.wrap(chars, 0, chars.length);
                System.out.println("String test = " + test);
                chars[0] = 'k';
                chars[1] = 'a';
                chars[2] = 'l';
                chars[3] = 'l';
                chars[4] = 'a';
                chars[5] = 'n';
                System.out.println("String test = " + test);
} Gil

How to create a xml file from String object in CS4

Hi All,
I want to convert a string object into an XML file using Javascript in Indesign CS4.
I have done the following script. But it does not convert the namespaces for the xml elements with no value in it.
var xml = new XML(string);
The value present in string is "<level_1 xsi:nil="true" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"/>"
When it is converted to xml, the value becomes "<level_1 xsi:nil="true"/>"
On processing the above xml object, am getting an error like this "Uncaught JavaScript exception: Unbound namespace prefix."
Kindly help.
Thanks,
Anitha

Can you post more of the script?
Are you getting the XML file from disk, or a string?

Why should I wrap String objects in a class for my HtmlDataTable?

Hi,
Let me describe a basic scenario in which my problem occurs. I have a backing bean and a JSP. The JSP gets a List<String> which is displayed inside a column in an editable HtmlDataTable. Each row in the data table has a UICommandLink that can perform an update to the value in the first column. Hence, the table only has two columns: one input field and one command link.
My problem is this: When I try to execute HtmlDataTable#getRowData() when the command link is pressed, the updated values are not retrieved, but instead the values that have been in the input field before any changes were made. However, if I instead wrap my List objects inside a StringWrapper class (with a String property and appropriate getters and setters) such that I have a List<StringWrapper>, the problem does not occur. Why is this and is there any way to avoid it?
I typed out some code to illustrate my scenario. Example 1 is where the table displays a list of String objects and Example 2 is where the table displays a list of StringWrapper objects.
Example 1: [http://pastebin.com/m2ec5d122|http://pastebin.com/m2ec5d122]
Example 2: [http://pastebin.com/d4e8c3fa3|http://pastebin.com/d4e8c3fa3]
I'll appreciate any feedback, many thanks!

Hi,
Let me describe a basic scenario in which my problem occurs. I have a backing bean and a JSP. The JSP gets a List<String> which is displayed inside a column in an editable HtmlDataTable. Each row in the data table has a UICommandLink that can perform an update to the value in the first column. Hence, the table only has two columns: one input field and one command link.
My problem is this: When I try to execute HtmlDataTable#getRowData() when the command link is pressed, the updated values are not retrieved, but instead the values that have been in the input field before any changes were made. However, if I instead wrap my List objects inside a StringWrapper class (with a String property and appropriate getters and setters) such that I have a List<StringWrapper>, the problem does not occur. Why is this and is there any way to avoid it?
I typed out some code to illustrate my scenario. Example 1 is where the table displays a list of String objects and Example 2 is where the table displays a list of StringWrapper objects.
Example 1: [http://pastebin.com/m2ec5d122|http://pastebin.com/m2ec5d122]
Example 2: [http://pastebin.com/d4e8c3fa3|http://pastebin.com/d4e8c3fa3]
I'll appreciate any feedback, many thanks!

How to validate the string object for alphabet input

Hi,
I want to check for alphabet (a-z,A-Z), in String object. I need to check the object, whether its contain numerals or special character, in that case, I want to throw an error stating that "value is not valid". It should accept only the a-z or A-Z.
how to do this.
Thanks in advance
Karthi

> I want to check for alphabet (a-z,A-Z), in String
object. I need to check the object, whether its
contain numerals or special character, in that case,
I want to throw an error stating that "value is not
valid". It should accept only the a-z or A-Z.
how to do this.
As Rene suggested, you can do this using the Pattern class:
http://java.sun.com/j2se/1.4.2/docs/api/java/util/regex/Pattern.html
You can do it also by looping through your String and check with String's charAt(index) method (which returns a char) to see if every char from the String is >= A AND <= z.
http://java.sun.com/j2se/1.4.2/docs/api/java/lang/String.html
Good luck.

"a"+"b"+"c", how many String objects created?

Hello everyone,
String s = "a" + "b" +"c";
How many String objects are created?
I guess 5, is it right?
regards

> How many String objects are created?
>
I guess 5, is it right?
Nope. Just one.

Declaring String object

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