I have a problem with a fairly simple question in Java. To repeat a string, you can use str.repeat from Java 11. However I have the following error:
Exception in thread "main" java.lang.Error: Unresolved compilation problem:
The method repeat(int) is undefined for the type String
The code is as follows:
String rep = "-";
rep = rep.repeat(4);
System.out.println(rep);
With a command-line compilation, no problem, but Eclipse is problematic, it uses
java-11-openjdk-amd64
Thanks for your help
repeat is Java 11 keyword. You are trying to use repeat from a lower version than Java 11.
modify the code with for loop as below.
String rep = "";
for(int i=0;i<4;i++) {
rep += "-";
}
System.out.println(rep);
Related
I am getting below error inspite of correct python code don't know how to resolve this error. Any help is much appreciated
org.apache.nifi.processor.exception.ProcessException: javax.script.ScriptException: SyntaxError: no viable alternative at input '*' in <script> at line number 35 at column number 26
python code
def get_match_list(regEx, line):
match = re.search(regEx, line)
print(match)
if match:
match_list = [*match.groups()] # this is the line exception is pointed
return match_list
else:
return []
It looks like jython use python 2.7 and as Unpacking Generalizations is a feature that introduced in python 3.5 you can not use this syntax in jython, so an alternative way to convert a tuple to a list is that use list ( match.groups) it works fine in older versions of python and current version of jython (2.7.2)
I have a very strange problem with NullPointerException. Code example is as follows:
...
... public String[] getParams(...) {
... ...
... ...
143 return new String[] {
144 getUserFullName(),
145 StringUtil.formatDate(sent),
. tiltu,
. StringUtil.initCap(user.getName()),
. vuosi.toString(),
. asiatyyppi[0] + " " + lisatiedot[0],
. asiatyyppi[1] + " " + lisatiedot[1],
. alaviitteet[0],
152 alaviitteet[1]};
153 }
Now, I have got an issue from production having a stack trace:
java.lang.NullPointerException
at package.EmailService.getParams(EmailService.java:143)
...
I am unable to produce that kind of stack trace myself. It maybe some environment issue that for some reason line numbers don't match. If I have null references on any variable stack trace points to that specific line but never to line 143.
But what I want to ask is: is it possible to produce NullPointerException at line 143 specifically?
The line number in the stack trace comes from the LineNumberTable attribute in the class file. (See JVM specification)
It would be no problem to output the right line number for a subexpression - all the compiler has to do is to say that from byte-code index x to y, there is a correspondence with source code line z.
But up to and including Java 1.7 there was a bug in the compiler, that was fixed in 1.8:
https://bugs.openjdk.java.net/browse/JDK-7024096
A DESCRIPTION OF THE PROBLEM : linenumbertable in compiled code only
has line numbers for starts of statements. When a statement is using
method chaining or other "fluent Interface" style API's a single
statement can span tens of lines and contain hundreds on method
invocations.
Currently an exception throw from within any of these methods will
have the linenumber of the first line of the enclosing statement which
makes it very hard to debug which method call is having a problem.
linnumbertable should have correct line numbers for every method
invocation.
--
BT2:EVALUATION
It seems simple enough to fix this, but its kinda risky at the end of
the jdk7 development cycle, targetting to jdk8.
So in 1.7, you would get the wrong reported line number for these kind of subexpressions (if they occurred within the same method though - if you invoked another method in a subexpression, and that other method caused a NullPointerException, you would see it reported there - this is probably why the bug isn't always a big problem)
One way you could work around this is by taking the Java 8 compiler to compile your source code, and use the flags javac -source 1.7 -target 1.7. But it would be better and safer to upgrade your prod environment to 1.8.
Consider your original code which defines a new String array:
return new String[] {
getUserFullName(),
StringUtil.formatDate(sent),
tiltu,
StringUtil.initCap(user.getName()),
vuosi.toString(),
asiatyyppi[0] + " " + lisatiedot[0],
asiatyyppi[1] + " " + lisatiedot[1],
alaviitteet[0],
alaviitteet[1]};
}
If any of the elements of the inline array should trigger a NullPointerException the JVM will interpret the Exception as having occurred on the line where the definition began. In other words, the JVM will view the above code as being the same as:
return new String[] { getUserFullName(), StringUtil.formatDate(sent), tiltu, StringUtil.initCap user.getName()), vuosi.toString(), asiatyyppi[0] + " " + lisatiedot[0], asiatyyppi[1] + " " + lisatiedot[1], alaviitteet[0], alaviitteet[1]}; }
where everything is on one line.
If you really want to handle NullPointerExceptions here, you should define the variables outside the instantiaition.
I'm trying to use the Eigen implementation of Levenberg Marquardt algorithm on a Android application. In order to use Eigen, I'm using Android NDK and jni. I've already tested Eigen with simple calculations (like matrix creation and vector sums) and it works perfectly. However, when I tried to use the Levenberg Marquardt algorithm I got some errors on the LevenbergMarquardt.h file from Eigen's library.
First, here is my code. I based on this code:
Eigen::MatrixXd matrix(count, 3);
for (int i = 0; i < count; i++) {
Eigen::VectorXd t(3);
t << x[i], y[i], accuracy[i];
matrix.row(i) = t;
}
distance_functor functor(matrix, count);
Eigen::NumericalDiff<distance_functor> numDiff(functor);
Eigen::LevenbergMarquardt<Eigen::NumericalDiff<distance_functor>,double> lm(numDiff);
lm.parameters.maxfev = 2000;
lm.parameters.xtol = 1.49012e-08;
lm.parameters.ftol = 1.49012e-08;
lm.parameters.gtol = 0;
lm.parameters.epsfcn = 0;
Eigen::LevenbergMarquardtSpace::Status ret = lm.minimize(poseResult);
And those are the error that I got. The first two errors are in Eigen's library, and the last one is on the LevenbergMarquardt object creation. I've also included the respective line of code of the error, following the message:
Invalid template
arguments LevenbergMarquardt.h /jnimath/jni/unsupported/Eigen/src/LevenbergMarquardt line
121 Semantic Error
typedef PermutationMatrix<Dynamic,Dynamic> PermutationType;
Invalid template
arguments LevenbergMarquardt.h /jnimath/jni/unsupported/Eigen/src/NonLinearOptimization line
103 Semantic Error
PermutationMatrix<Dynamic,Dynamic> permutation;
Invalid template arguments test.cpp /jnimath/jni line 47 Semantic
Error
Eigen::LevenbergMarquardt,double> lm(numDiff);
The first two errors are really strange because there are some other typedefs using Dynamic and they are not throwing errors.
Also, I noticed that I got some symbol errors on the compilation, which are:
Symbol
'YOU_MIXED_DIFFERENT_NUMERIC_TYPES__YOU_NEED_TO_USE_THE_CAST_METHOD_OF_MATRIXBASE_TO_CAST_NUMERIC_TYPES_EXPLICITLY'
could not be resolved Matrix.h /jnimath/jni/Eigen/src/Core line
277 Semantic Error
Symbol 'YOU_TRIED_CALLING_A_VECTOR_METHOD_ON_A_MATRIX' could not be
resolved Matrix.h /jnimath/jni/Eigen/src/Core line 224 Semantic Error
So, I have two questions:
Why am I getting errors on those lines?
Does anyone know how to fix that problem?
Thank you
After learning Lambda Expressions in Java, I tried to practice some simple examples. But in my first example only I am getting the following error.
Exception in thread "main" java.lang.IncompatibleClassChangeError
at java.lang.invoke.MethodHandleNatives.linkMethodHandleConstant(MethodHandleNatives.java:384)
at com.example.lambda.HelloLambda.main(HelloLambda.java:15)
Caused by: java.lang.NoSuchMethodException: no such method: java.lang.invoke.LambdaMetafactory.metaFactory(Lookup,String,MethodType,MethodHandle,MethodHandle,MethodType)CallSite/invokeStatic
at java.lang.invoke.MemberName.makeAccessException(MemberName.java:763)
at java.lang.invoke.MemberName$Factory.resolveOrFail(MemberName.java:880)
at java.lang.invoke.MethodHandles$Lookup.resolveOrFail(MethodHandles.java:1019)
at java.lang.invoke.MethodHandles$Lookup.linkMethodHandleConstant(MethodHandles.java:1284)
at java.lang.invoke.MethodHandleNatives.linkMethodHandleConstant(MethodHandleNatives.java:382)
... 1 more
Caused by: java.lang.NoSuchMethodError: java.lang.invoke.LambdaMetafactory.metaFactory(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
at java.lang.invoke.MethodHandleNatives.resolve(Native Method)
at java.lang.invoke.MemberName$Factory.resolve(MemberName.java:852)
at java.lang.invoke.MemberName$Factory.resolveOrFail(MemberName.java:877)
... 4 more
The error seems an error because of backward compatibility issue. But don't know how to fix this. Many answers in StackOverFlow suggested Recompilation could fix this issue. But still I am getting this error.
My code
package com.example.lambda;
public class HelloLambda {
static String firstname = "ChanSek";
static String lastname = "Nayak";
interface HelloService {
String hello();
}
public static void main(String[] args) {
HelloService helloService =
() -> {String hello="Hello " + firstname + " " + lastname;
return hello;};
System.out.println(helloService.hello());
}
}
The code compiles fine. But running gives the above mentioned error.
I am using JDK1.8.0 snapshot.
Is it possibly because of this?
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8019635
The way lambdas have been done in Java 8 has changed, very recently (07/2013), in a not backwards compatible way.
If you've somehow managed to compile with a compiler which talks PRE beta 103 lambdas, but are running with a JRE of POST 103 lambdas, you'll have problems.
(The hint for me here is that the metafactory name used to be mixed case, but in java 1.8.0 beta 103 appears to be lower case - you're searching for mixed case, but not finding it.)
In cpp file I have std::round(double)
Please can I know the equivalent code in Java
Edit: I am already using java.lang.Math.round(double) and getting match in 99% cases. But in some places iam getting mismatch. For example:
std::round(4816.5058) = 4816 and Math.round(4816.5058) = 4817
std::round(4466.49996) = 4467 and Math.round(4466.49997) = 4466
java.lang.Math.round(double)