Doubt with String class
Please tell me why String class objects are immutable. Why it was designed like that?
Read Java tutorials.Thanks for your reply. But tutorial says thatString
objects are immutable but they dont say why
they
made
as immutable.Welcome swathi.reply #4 is the best answer Ithink.
But please look at my reply #8Please look at reply#2 in the other thread.But reply #2 was mine. I dont understand what you say? Please help me.
Similar Messages
-
Problems with String[] Class Object
Hi guys,
I'm writing a web server who should invoke a method of a class when asked by a client.
My problem is that if the method that should be invoked has a String[] parameter the web server is unable to invoke it and throws a java.lang.IllegalArgumentException: argument type mismatch.
Useful pieces of code to understand are the following:
//create the Class[] to pass as parameter to the getMethod method
Class[] paramType = {String[].class};
//find the class "className" and create a new instance
Class c = Class.forName(className);
Object obj = c.newInstance();
//the getMethod should find in the class c the method called nameMeth
// having paramType (i.e. String[]) as parameter type...
Method theMethod = c.getMethod(nameMeth, paramType);
//here's the problematic call!!
theMethod.invoke(obj, params);I've noted that System.out.println(theMethod); prints the signature of the method with the parameter type java.lang.String[].
System.out.println(paramType[0]); instead prints [Ljava.lang.String;
I know that [L means that it is an array, so why do you think that I'm having an argument type mismatch?
Thank youI had no problems making that work.import java.lang.reflect.Method;
public final class StringArray {
public static final String CLASSNAME = "StringArray";
public static final String METHODNAME = "myMethod";
public static final String[] sa = { "a", "b"};
// automatic no-args constructor
public final void myMethod(String[] sa) {
for(int i=0;i<sa.length;++i) {
System.out.println(sa);
public static final void main(String[] arg) throws Exception {
//create the Class[] to pass as parameter to the getMethod method
Object[] params = { sa };
Class[] paramType = {sa.getClass()};
//find the class "className" and create a new instance
Class c = Class.forName(CLASSNAME);
Object obj = c.newInstance();
//the getMethod should find in the class c the method called nameMeth
// having paramType (i.e. String[]) as parameter type...
Method theMethod = c.getMethod(METHODNAME, paramType);
//here's the problematic call!!
theMethod.invoke(obj, params); -
What is the exact difference between
String s=new String("xxxxxxx");
String s="xxxxxxx"; ?
Please let me know
rgds
Mohan SRead the Java Language Specs people.
If I do this:
String a = "A";
String b = "A";How many "A"'s are in memory?
The answer: 1.
Doing this:
String a = new String("A");First thing that happens is that "A" will be put in memory. Then a reference to "A" will be created (new String()), then your creating a reference (String a) and assigning your new String to it.
The new String() creates a new object referencing the same string in memory.
Hope this clarifies.
It's explained better in JLS
3.10.5 String Literals
4.3.3 The Class String
And the VM Spec
2.3 Literals
String literals and, more generally, strings that are the values of constant expressions are "interned" so as to share unique instances, using the method String.intern. -
[svn:osmf:] 11239: Updated DRM MediaError codes to work with the the Framework strings class.
Revision: 11239
Author: [email protected]
Date: 2009-10-28 13:03:06 -0700 (Wed, 28 Oct 2009)
Log Message:
Updated DRM MediaError codes to work with the the Framework strings class. DRM errors spit directly from the VideoElement.
Modified Paths:
osmf/trunk/framework/MediaFramework/org/osmf/events/MediaErrorCodes.as
osmf/trunk/framework/MediaFramework/org/osmf/utils/MediaFrameworkStrings.as
osmf/trunk/framework/MediaFramework/org/osmf/video/VideoElement.ascheck the server log;
/app/oracle/product/fwm11g/user_projects/domains/fwm_domain/servers/AdminServer/logs/AdminServer.log
you can launch the console and see if it is running; http://<server>:<port>/console -
Did the Java Writers Get a Little Happy with Memory Use in String class?
I mean that question half jokingly.
Taking a look at the String class code, I saw the following (below).
Why is there an int for offset and an int for count?
String is immutable, why not just return value.length for the count?
And what is the offset for?
Thanks!
public final class String
implements java.io.Serializable, Comparable<String>, CharSequence
/** The value is used for character storage. */
private final char value[];
/** The offset is the first index of the storage that is used. */
private final int offset;
/** The count is the number of characters in the String. */
private final int count;
/** Cache the hash code for the string */
private int hash; // Default to 0PS: a second look kinda verifies it too.
in the constructor ,count is even defined as value.length.
public String(char value[]) {
int size = value.length;
this.offset = 0;
this.count = size;
this.value = Arrays.copyOf(value, size);
}You don't get the choice. The arrays are shared
whenever you do substring.Yea, thats my point. I think most Strings are unique.
Id be very surprised if even 2% of all String use was
a result of a substring.The wrapper classes use it for parsing.
File uses it for getName and getParent.
String uses it for trim.
Class uses it for resolving names.
Regex uses it.
etc. ...
Now, I don't know what percentage of usage all that amounts to, but it IS heavily used.
So your desire to gain the 2 bytes back would cost enough byte every time substring is used that it might end up costing far more than the 8 bytes you save. -
Hello
I have a doubt about string.intern() method.
The document says
When the intern method is invoked, if the pool already contains a string equal to this String object as determined by the String.equals(Object) method, then the string from the pool is returned.
So what is the point of using this intern() method with == or != operators if it aleady calling to equals method internally?
eg:
if (studentObject.getName().intern() == "Student Name") {}cannot be better than
if (studentObject.getName().equals("Student Name")) {}Can someone please explain?Easy dude.
>
Why do you need to optimize it?>
Because i want to.
I would avoid the whole stupid 100 line if-else by doing a Map of type->object and then just clone() the object. But maybe that might not be suitable or "fast enough" for you.I cannot do above because object have it's own behaviors varying at run time
eg - class One has setOne method and class hundred has setHundred method
. Even if i use a map and clone it again i have to use above comparison for setting those behaviours.
Explain your actual problem you're trying to solve, with actual cases. What are these "one" and "Hundred" classes really? Or is your project so top secret that you can't tell us?It is not secret but big. And I need to make the question understandable. If I post the whole code no one will looking at it.
Now you asking so please have a look.
still I have cleaned up many.
My initial question was how to bit speed up the comparison? And can't i use intern() Because here if I got plenty of rectangles(it is the last) performace sucks.
for (CObject aObject : objList) {
if (aObject.getType().equals(SConstant.TEMPLATE)) { /* process Template */
Template tObj = (Template) aObject;
org.apache.velocity.Template template = VelocityTemplateManager.getInstance().getObjectTemplateFromFile(retemplateProperties.getProperty("PAGE"));
VelocityContext context = new VelocityContext();
StringWriter writer = new StringWriter();
context.put(retemplateProperties.getProperty("BAND_OBJECT"), dtmBand);
tObj.setTags(writer.toString());
} else if (aObject.getType().equals(SConstant.LINE)
&& !isInBandandBandAutoAdjust(aObject)) {
Line object = (Line) aObject;
org.apache.velocity.Template template = VelocityTemplateManager.getInstance().getObjectTemplateFromFile(retemplateProperties.getProperty("LINE"));
VelocityContext context = new VelocityContext();
StringWriter writer = new StringWriter();
updateContextWithCheckShifting(context, object);
context.put(retemplateProperties.getProperty("LINE_OBJECT"), object);
template.merge(context, writer);
object.setTags(writer.toString());
} else if (aObject.getType().equals(SConstant.IMAGE) /* process Image */
&& !isInBandandBandAutoAdjust(aObject)) {
REImage imageObject = (REImage) aObject;
org.apache.velocity.Template template = VelocityTemplateManager.getInstance().getObjectTemplateFromFile(retemplateProperties.getProperty("IMAGE"));
VelocityContext context = new VelocityContext();
updateContextWithCheckShifting(context, imageObject);
context.put(retemplateProperties.getProperty("IMAGE_OBJECT"), imageObject);
mageObject.setTags(writer.toString());
else if (aObject.getType().equals(SConstant.RECTANGLE) /* process Rectangle */
&& !isInBandandBandAutoAdjust(aObject)) {
Rectangle rectangleObject = (Rectangle) aObject;
org.apache.velocity.Template template = VelocityTemplateManager.getInstance().getObjectTemplateFromFile(retemplateProperties.getProperty("RECTANGLE"));
VelocityContext context = new VelocityContext();
StringWriter writer = new StringWriter();
updateContextWithCheckShifting(context, rectangleObject);
context.put(retemplateProperties.getProperty("RECTANGLE_OBJECT"), rectangleObject);
template.merge(context, writer);
rectangleObject.setTags(writer.toString());
}And masijade
Thank you very much for the better explanation. -
How to find out what are the functions supported by string class
Hi,
Can any one let me know how to find what are all the functions supported by the string class in standard(STL) library on solaris.
Regards,
Vignesh1. Any C++ textbook that covers the Standard Library will tell you about the standard string class. A good tutorial and reference for the entire Standard Library is "The C++ Standard Library" by Nicolai Josuttis, published by Addison Wesley.
2. WIth Sun C++, the command
man -s3C++ basic_string
provides documentation for the default libCstd version of the Standard Library.
3. You could look at the <string> header itself. I don't recommend that approach. -
We have developed our application in Solaris 10 environment. While running Purify on that it shows leak in the string class. This leak is incremental and so process size keeps in increasing. If we replace string with char array, the leaks disappears and process size also becomes stable.
Following is the snapshot of the memory leak stack reported by Purify:
MLK: 4505 bytes leaked in 85 blocks
* This memory was allocated from:
malloc [rtlib.o]
operator new(unsigned) [libCrun.so.1]
void*operator new(unsigned) [rtlib.o]
__rwstd::__string_ref<char,std::char_traits<char>,std::allocator<char> >*std::basic_string<char,std::char_traits<char>,std::allocator<char> >::__getRep(unsigned,unsigned) [libCstd.so.1]
char*std::basic_string<char,std::char_traits<char>,std::allocator<char> >::replace(unsigned,unsigned,const char*,unsigned,unsigned,unsigned) [libCstd.so.1]
std::basic_string<char,std::char_traits<char>,std::allocator<char> >&std::basic_string<char,std::char_traits<char>,std::allocator<char> >::operator=(const char*) [libCstd.so.1]
Has anyone faced this problem earlier or is there any patch available for this?Over time, we have found and fixed memory leaks in the C++ runtime libraries.
Get the latest patches for the compiler you are using. (You didn't say which one.) You can find all patches here:
[http://developers.sun.com/sunstudio/downloads/patches/index.jsp]
Also get the latest Solaris patch for the C++ runtime libraries, listed on the same web page.
If that doesn't fix the problem, please file a bug report at
[http://bugs.sun.com]
with a test case that can be compiled and run to demonstrate the problem. -
Problem with loading classes!!!
I am loading classes using
// Open File
InputStream jarFile = new BufferedInputStream(new FileInputStream(
pluginPath));
// Get Manifest and properties
Attributes attrs = new JarInputStream(jarFile).getManifest().
getMainAttributes();
jarFile.close();
// Read Main Class
String mainClass = attrs.getValue("Protocol-Class");
// Load all classes from jar file without giving classpath
URL url = new URL("jar:file:" + pluginPath + "!/");
JarURLConnection jarConnection = (JarURLConnection) url.openConnection();
URL[] urls = new URL[] {
url};
ClassLoader classLoader = new URLClassLoader(urls);
// Create new instance of protocol
Protocol protocol = (Protocol) classLoader.loadClass(mainClass).
newInstance();
I am loading classes one by one say a order A, B, C. In my case class c extends class A. So I am loading class A first and later B and finally C. But I am getting exceptions when loading class C that Class A is unknown.The following exception is thrown
java.lang.NoClassDefFoundError: com/a/A at java.lang.ClassLoader.defineClass0(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:537)
Please give me a solution to make it run.You create a new class loader for each class. The class loaders are independent, and so the class hierarchies they load are independent. Class A loader by classLoaderOne doesn't see class B loader by classLoaderTwo - they are loaded into their own sandboxes.
Either load everything with one class loader or create the class loaders in a hierarchy. To create a hierarchy use the class loader constructor that takes a parent class loader as a parameter. One class loader may be easier because then you don't need to worry about loading order. -
Getting problem with DOMImplementation classes method getFeature() method
hi
getting problem with DOMImplementation classes method getFeature() method
Error is cannot find symbol getFeature()
code snippet is like...
private void saveXml(Document document, String path) throws IOException {
DOMImplementation implementation = document.getImplementation();
DOMImplementationLS implementationLS = (DOMImplementationLS) (implementation.getFeature("LS", "3.0"));
LSSerializer serializer = implementationLS.createLSSerializer();
LSOutput output = implementationLS.createLSOutput();
FileOutputStream stream = new FileOutputStream(path);
output.setByteStream(stream);
serializer.write(document, output);
stream.close();
problem with getFeature() methodYou are probably using an implementation of DOM which does not implement DOM level-3.
-
ok, i know extending the string class is illegal because it's final, but i want to make an advanced string class that basically "extends" the string class and i've seen online this can be done through wrapper classes and/or composition, but i'm lost
here is my sample code that is coming up with numerous compile time errors due to the fact that when i declare a new AdvString object, it doesn't inherit the basic string features (note: Add is a method that can add a character to a specified location in a string)
class AdvString
private String s;
public AdvString(String s)
this.s = s;
public void Add(int pos, char ch)
int this_len = (this.length()) + 1;
int i;
for(i=0;i<(this_len);i++)
if(pos == i)
this = this + ch;
else if(pos < i)
this = this + this.charAt(i-1);
else
this = this + this.charAt(i);
public static void main(String[] args)
AdvString s1;
s1 = new AdvString("hello");
char c = 'x';
int i = 3;
s1.Add(i,c);
//s2 = Add(s1,i,c);
//String s2_reversed = Reverse(s2);
System.out.println("s1 is: " + s1);
any tips?see REString at,
http://www.geocities.com/rmlchan/mt.html
you will have to replicate all the String methods you are interested in, and just forward it to the String instance stored in REString or the like. it is like a conduit class and just passes most processing to the 'real' string. maybe a facade pattern. -
How to read a xml file with StringReader class
Hi,
I need to read a XML document with StringReade class. My aplication receives an absolute path but this doesn't work:
StringReader oStringReader =
new StringReader(c:\java\libros.xml);
However it works with:
StringReader oStringReader =
new StringReader("<?xml version="1.0" e......");
ie, with the whole document as a String, but I need to do it as the frist way.
ThanksHi,
I need to read a XML document with StringReade class.
My aplication receives an absolute path but this
doesn't work:
StringReader oStringReader =
new StringReader(c:\java\libros.xml);
However it works with:
StringReader oStringReader =
new StringReader("<?xml version="1.0" e......");
ie, with the whole document as a String, but I need
to do it as the frist way.
Thankstake a look at this link:
http://java.sun.com/webservices/jaxp/dist/1.1/docs/tutorial/sax/2a_echo.html -
Java Switch Statement with Strings
Apparently you cant make a switch statement with strings in java. What is the most efficient way to rewrite this code to make it function similar to a swtich statement with strings?
switch (type){
case "pounds":
type = "weight";
break;
case "ounces":
type = "weight";
break;
case "grams":
type = "weight";
break;
case "fluid ounces":
type = "liquid";
break;
case "liters":
type = "liquid";
break;
case "gallons":
type = "liquid";
break;
case "cups":
type = "liquid";
break;
case "teaspoons":
type = "liquid";
break;
case "tablespoons":
type = "liquid";
break;
}I'd create a Map somewhere with entries "liquid", "weight", etc.
public class Converter {
private static Map<String, List<String>> unitMap = new HashMap<String, List<String>>();
private static String[] LIQUID_UNITS = { "pints", "gallons", "quarts", "millilitres" };
private static String[] WEIGHT_UNITS = { "pounds", "ounces", "grams" };
static {
List<String> liquidUnits = new ArrayList<String>();
for (int i = 0; i < LIQUID_UNITS.length; i++) liquidUnits.add(LIQUID_UNITS));
unitMap.put("liquid", liquidUnits);
... // other unit types here
public String findUnitType(String unit) {
for (String unitType : unitMap.keySet()) {
List<String> unitList = unitMap.get(unitType);
if (unitList.contains(unit))
return unitType;
return null;
It might not be more "efficient", but it's certainly quite readable, and supports adding new units quite easily. And it's a lot shorter than the series of if/else-ifs that you would have to do otherwise. You'll probably want to include a distinction between imperial/metric units, but maybe you don't need it.
Brian -
I think this is a Bug of String class
I think this is a Bug of String class, do you agree with me ?
String s = "1234........"; // when "1234........". length() > 65535, there will be wrong, but
char[] c = new char[88888];...
String s = new String(c);even if c.length >65535�Cevery thing is ok.
so I think is a bug. Somebody give me a answer, thanksbelow is the two Constructors Of String
public String(String original) {
int size = original.count;
char[] originalValue = original.value;
char[] v;
if (originalValue.length > size) {
// The array representing the String is bigger than the new
// String itself. Perhaps this constructor is being called
// in order to trim the baggage, so make a copy of the array.
v = new char[size];
System.arraycopy(originalValue, original.offset, v, 0, size);
} else {
// The array representing the String is the same
// size as the String, so no point in making a copy.
v = originalValue;
this.offset = 0;
this.count = size;
this.value = v;
}=====================
public String(char value[]) {
int size = value.length;
char[] v = new char[size];
System.arraycopy(value, 0, v, 0, size);
this.offset = 0;
this.count = size;
this.value = v;
}I don't know where has the problem. -
How to implement the String class "split()" method (JDK1.4) in JDK 1.3
is it possible , with some code, to implement the split() method of the String class......which is added in JDK1.4 ..... in JDK1.3
would be helpful if anyone could suggest some code for this...Here it is
public static String[] split(String source, char separ){
answer=new Vector();
int position=-1, newPosition;
while ((newPosition=source.indexOf(separ,position+1))>=0){
answer.add(source.subString(position+1,newPosition));
position=newPosition;
} //while
answer.add(source.subString(position+1,source.length-1);
return (String[])(answer.toArray());
} //split
Maybe you are looking for
-
NFe - Obrigatoriedade da chave de acesso nas NFs de entrada.
Olá Verificando no Site do SPED temos a nova alteração abaixo para Janeiro/2012 http://www1.receita.fazenda.gov.br/noticias/2011/setembro/noticia-23092011.htm "Disponibilizada a versão 2.0.6 do Guia Prático da EFD (Art. 1º do Ato COTEPE ICMS 41/11).
-
How to get Win NT userid for setting VPD application context?
We are planning to implement row-level security using VPD. For that to happen, we need to capture the Windows NT userid since all the applications connect through a generic Oracle userid which will not help us. Has anyone done this before? Your respo
-
i write such code double a = 4.3 double b = 3 System.out.println(a*b) why return value is 12.8999999999999 how to make it return right string?Please help me!
-
I have a music docking station with an 8 pin connection. My i-pod has a 30 pin connection. Is there an adaptor available?
-
Conversion of file into byteStream
Hi , (1)I want to convert any file type into ByteStream and print all byte . Can anyone send me java program. (2) Can I encript my file using ByteStream. Thanks