Exception in thread main java lang error unresolved compilation problem arrays cannot be resolved

The exception in thread “main” java.lang.error: unresolved compilation problem: usually occurs due to syntax or typographical errors. Also, you might get the same exception due to using unknown or undefined classes and modules. Surprisingly, this article will let you know about all the possible causes in detail.

Read on to find out the most relevant cause and solve it at the earliest.

The unresolved compilation problems occur because of syntax mistakes and typos. Moreover, using unknown or undefined classes and modules throw the same error. Please go through the causes described below to better understand the issues:

– The Class or Module Is Not Imported

If you use a class or module without importing the same in your program, then you’ll get the said java lang error. It indicates that you are instantiating a class or using a module that is unknown to the stated program.

– Using Non-existent Classes

If you use a class that isn’t already defined, then the same exception will pop up on your screen.

– A Syntax Error Resulting in Exception in Thread “main” java.lang.error: Unresolved Compilation Problem:

Even a common syntax error such as a missing or an extra curly bracket “{“ or a semicolon “;” can output the said exception. It includes sending the wrong arguments while calling the functions.

The below example code highlights the above-stated syntax errors:

public class myClass{
public static void main(String[] args){
anotherClass obj2 = new anotherClass();
obj2.myFunc(“Three”)
}
public class anotherClass{
public String myFunc(int num){
System.out.println(“You have entered:” + num);
}
}

– A Typographical Error

Another common cause behind the java lang error can be a typographical error. It usually happens when you code in hurry without realizing that you’ve typed the variable or function name incorrectly.

For example, you will get the above error if you have accidentally called the println() function as pirntln().

How To Fix the Compilation Exception?

Here are the easy-to-implement working solutions to lower your frustration level and resolve the said exception.

– Import the Necessary Classes and Modules

Look for the classes and modules used in your program. Next, import the given classes and modules. The stated simple step will kick away the exception if it is related to the classes and modules.

– Remove or Replace the Undefined Classes

You must remove the code that instantiates the undefined classes. Also, if you intended to call another class, then replacing the class name with a valid class name will work too.

– How To Resolve Java Lang Error in Eclipse?

You can notice the warnings shown in the Eclipse to identify the mistakes and correct them. Consequently, you will resolve the resulting java lang error.

– Use an Integrated Development Environment (IDE)

Using an IDE is the best possible solution to make the java lang error go away. It is because you’ll be notified regarding the typos and syntax errors. Moreover, you’ll be informed about the unknown modules and classes. You can then easily make the corrections and import the required classes or modules.

The above solution will let you skip the double-checking step before executing the code.

FAQ

The following questions might be disturbing you. So, here are the simplest answers to clear your confusion.

– What Is Unresolved Compilation Problem Java?

The above problem tells that there is a compilation error in the code. Although it is a generic error, you can learn more about it through the error description.

– What Is Exception in Thread Main Java Lang Error?

The stated exception tells that an error has occurred in the thread that is running the Java application. You can say that the given exception points towards the location of the error.

Wrapping Up

Now, it’s clear to you that the compilation error pops up due to common coding mistakes. Also, you get the said exception when the compiler isn’t aware of the classes and modules that are being used in your program. Plus, here is the list of fixing procedures obtained from the above article to make the long talk short:

• You should import all the necessary classes and modules in your program
• You should use only valid classes and modules
• Using the IDE can help you in determining and correcting most of the coding mistakes that help in fixing the java lang error

Indeed, the given exception seems to be complicated but it doesn’t demand anything else except for the careful investigation of the code.

Scanner cannot be resolved to a type

I just installed Ubuntu 8.04 and I’m taking a course in Java so I figured why not install a IDE while I am installing it. So I pick my IDE of choice, Eclipse, and I make a very simple program, Hello World, to make sure everything is running smoothly. When I go to use Scanner for user input I get a very odd error:

6 Answers 6

The Scanner class is new in Java 5. I do not know what Hardy’s default Java environment is, but it is not Sun’s and therefore may be outdated.

I recommend installing the package sun-java6-jdk to get the most up-to-date version, then telling Eclipse to use it.

If you are using a version of Java before 1.5, java.util.Scanner doesn’t exist.

Which version of the JDK is your Eclipse project set up to use?

Have a look at Project, Properties, Java Build Path — look for the ‘JRE System Library’ entry, which should have a version number next to it.

It could also be that although you are have JDK 1.5 or higher, the project has some specific settings set that tell it to compile as 1.4. You can test this via Project >> Properties >> Java Compiler and ensure the «Compiler Compliance Level» is set to 1.5 or higher.

I know, It’s quite a while since the question was posted. But the solution may still be of interest to anyone out there. It’s actually quite simple.

Under Ubuntu you need to set the java compiler «javac» to use sun’s jdk instead of any other alternative. The difference to some of the answers posted so far is that I am talking about javac NOT java. To do so fire up a shell and do the following:

1. As root or sudo type in at command line:

# update-alternatives —config javac

Locate the number pointing to sun’s jdk, type in this number, and hit «ENTER».

Источник

Java: Unresolved compilation problem

What are the possible causes of a «java.lang.Error: Unresolved compilation problem»?

I have seen this after copying a set of updated JAR files from a build on top of the existing JARs and restarting the application. The JARs are built using a Maven build process.

I would expect to see LinkageErrors or ClassNotFound errors if interfaces changed. The above error hints at some lower level problem.

A clean rebuild and redeployment fixed the problem. Could this error indicate a corrupted JAR?

10 Answers 10

Summary: Eclipse had compiled some or all of the classes, and its compiler is more tolerant of errors.

The default behavior of Eclipse when compiling code with errors in it, is to generate byte code throwing the exception you see, allowing the program to be run. This is possible as Eclipse uses its own built-in compiler, instead of javac from the JDK which Apache Maven uses, and which fails the compilation completely for errors. If you use Eclipse on a Maven project which you are also working with using the command line mvn command, this may happen.

The cure is to fix the errors and recompile, before running again.

The setting is marked with a red box in this screendump:

try to clean the eclipse project

you just try to clean maven by command

and after that following command

and rebuild your project.

Your compiled classes may need to be recompiled from the source with the new jars.

Try running «mvn clean» and then rebuild

The major part is correctly answered by Thorbjørn Ravn Andersen.

This answer tries to shed light on the remaining question: how could the class file with errors end up in the jar?

Each build (Maven & javac or Eclipse) signals in its specific way when it hits a compile error, and will refuse to create a Jar file from it (or at least prominently alert you). The most likely cause for silently getting class files with errors into a jar is by concurrent operation of Maven and Eclipse.

If you have Eclipse open while running a mvn build, you should disable Project > Build Automatically until mvn completes.

EDIT: Let’s try to split the riddle into three parts:

(1) What is the meaning of «java.lang.Error: Unresolved compilation problem»

This has been explained by Thorbjørn Ravn Andersen. There is no doubt that Eclipse found an error at compile time.

(2) How can an eclipse-compiled class file end up in jar file created by maven (assuming maven is not configured to used ecj for compilation)?

This could happen either by invoking Maven with no or incomplete cleaning. Or, an automatic Eclipse build could react to changes in the filesystem (done by Maven) and re-compile a class, before Maven proceeds to collect class files into the jar (this is what I meant by «concurrent operation» in my original answer).

(3) How come there is a compile error, but mvn clean succeeds?

Again several possibilities: (a) compilers don’t agree whether or not the source code is legal, or (b) Eclipse compiles with broken settings like incomplete classpath, wrong Java compliance etc. Either way a sequence of refresh and clean build in Eclipse should surface the problem.

Источник

Class file uses import but reports Unresolved compilation problems

I am having an issue resulting in the «Unresolved compilation problems» error. I have looked at this SO question, as well as this one of the same nature and finally this one again describing the same error.

All three of those describe dealing with compilation errors, but when I compile my project’s class files, either using Maven from inside eclipse, Maven from the command line, or just the javac command, no errors are reported.

We have a custom class, JmxTools, which uses import org.apache.commons.modeler.Registry; Now the source file does not complain about a missing import.

An answer to a similar question suggests looking at the «Problems» view in eclipse. This shows no errors

So, everything compiles fine, the commons-modeler jar is in my Maven dependencies. Yet when I run my web app and call the page using the JmxTools class I receive the following error stack:

How do I get around this? This is something I have not run into before and the answers to similar questions do not appear to apply to this situation

Following Kayaman’s advice:

1. Checked the war file and the commons-modeler jar file is present in WEB-INF/lib
2. Moved the commons-modeler jar from from the war to my tomcat’s lib/ folder
3. did a fresh clean, then compile, the package from the command line

Unfortunately, none of these helped the situation. I am still receiving the error.

Источник

Why do I get this error in Java? Exception in thread «main» java.lang.Error: Unresolved compilation problems

I constantly get the following error when running this code:

«Exception in thread «main» java.lang.Error: Unresolved compilation problems: linearequationproblem cannot be resolved to a type linearequationproblem cannot be resolved to a type at linearequationproblemredo.main(linearequationproblemredo.java:86)»

2 Answers 2

A class can be instantiated via the constructor . so you need to make linearequationproblem as a constructor like below.

I think you are completely new in Java. A good starting point is Java Tutorials and then move on to Oracle Java Tutorials

This code wont compile and these are the problems:

The class name is lineequation and the constructor name is linearequationproblem, which is not allowed. In Java class name and constructor name should be same, since constructor is a special method for creating the instance of the class and initializing the member variables.

Line 56: java linearequationproblem test = new linearequationproblem(in[0], in[1], in[2], in[3], in[4], in[5]); You are trying to create and instance of linearequationproblem but this type (Class) does not exists.

private double f;` That backtick is not legit and will fail to compile, since this is not a correct syntax.

You can refer the docs above for more details about Java. Enjoy Learning !

Источник

Exception in thread «main» java.lang.Error: Unresolved compilation problems: JNI4net

I am working with JNI4net and although the libraries and installed in the build path and eclipse recognizes them, it still gives me run time error. Why could that be in your opinion? Here is the code.

AND here is the message I get!

1 Answer 1

To make your life easier, I am going to share my findings here. Read Martin Serrano’s answer to my question. It will help you understand what needs to be done. Then go to jni4net’s website and download their example zip folder. Extract that. There is an example there called myCSharpDemoCalc. Replace your dll with myCSharpDemoCalc.dll (inside work folder) and then run generateProxies.cmd (be sure to edit this file to your dll name) and run.cmd. Then go to the work folder and run build.cmd (edit name) to create your JAR file. It might not spit out the j4n.dll you probably need to twik the path yourself. Use this JAR file. This was the easiest way to create a JAR file from a third party dll for me.

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Источник

Errors in Java occur when a programmer violates the rules of Java programming language.

It might be due to programmer’s typing mistakes while developing a program. It may produce incorrect output or may terminate the execution of the program abnormally.

For example, if you use the right parenthesis in a Java program where a right brace is needed, you have made a syntax error. You have violated the rules of Java language.

Therefore, it is important to detect and fix properly all errors occurring in a program so that the program will not terminate during execution.

Types of Errors in Java Programming

When we write a program for the first time, it usually contains errors. These errors are mainly divided into three types:

1. Compile-time errors (Syntax errors)
2. Runtime errors
3. Logical errors

Compile-time errors occur when syntactical problems occur in a java program due to incorrect use of Java syntax.

These syntactical problems may be missing semicolons, missing brackets, misspelled keywords, use of undeclared variables, class not found, missing double-quote in Strings, and so on.

These problems occurring in a program are called syntax errors in Java.

Since all syntax errors are detected by Java compiler, therefore, these errors are also known as compile time errors in Java.

When Java compiler finds syntax errors in a program, it prevents the code from compile successfully and will not create a .class file until errors are not corrected. An error message will be displayed on the console screen.

These errors must be removed by debugging before successfully compile and run the program. Let’s take an example program where we will get a syntax error.

Program source code 1:

public class CompileTimeErrorEx 
{
public static void main(String[] args) 
{
  System.out.println("a") // Syntax error. Semicolon missing.
 }
}

Compile time error in Java code:
      Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
      Syntax error, insert ";" to complete BlockStatements

When you will try to compile the above program, Java compiler will tell you where errors are in the program. Then you can go to the appropriate line, correct error, and recompile the program.

Let’s create a program where we will try to call the undeclared variable. In this case, we will get unresolved compilation problem.

Program source code 2:

public class MisspelledVar 
{	
public static void main(String[] args) 
{
int x = 20, y = 30;

// Declare variable sum.
   int sum = x + y; 

// Call variable Sum with Capital S.
   System.out.println("Sum of two numbers: " + Sum); // Calling of undeclared variable.
 }
}

Compile time error in Java code:
       Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
	Sum cannot be resolved to a variable

Program source code 3: Missing parenthesis in for statement.

public class MissingBracket 
{	
public static void main(String[] args) 
{ 
 int i; 
 int sum = 0;

// Missing bracket in for statement.
 for (i = 1; i <= 5; i++ // insert " ) Statement" to complete For Statement.
 {
   sum = sum + i;	
 }
System.out.println("Sum of 1 to 5 n");
System.out.println(sum); 
  }
}

Compile time error in Java code:
      Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
      Syntax error, insert ") Statement" to complete ForStatement

Program source code 4: Missing double quote in String literal.

public class MissingDoubleQuote
{	
public static void main(String[] args) 
{ 
 String str = "Scientech; // Missing double quote in String literal.
 System.out.println(str);
  }
}

Compile time error in Java code:
       Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
	String literal is not properly closed by a double-quote

We may also face another error related to the directory path. An error such as

javac : command not found

means that you have not set the path correctly.

Runtime Errors in Java

Runtime errors occur when a program is successfully compiled creating the .class file but does not run properly. It is detected at run time (i.e. during the execution of the program).

Java compiler has no technique to detect runtime errors during compilation because a compiler does not have all of the runtime information available to it. JVM is responsible to detect runtime errors while the program is running.

Such a program that contains runtime errors, may produce wrong results due to wrong logic or terminate the program. These runtime errors are usually known as exceptions.

For example, if a user inputs a value of string type in a program but the computer is expecting an integer value, a runtime error will be generated.

The most common runtime errors are as follows:

1. Dividing an integer by zero.
2. Accessing an element that is out of range of the array.
3. Trying to store a value into an array that is not compatible type.
4. Passing an argument that is not in a valid range or valid value for a method.
5. Striving to use a negative size for an array.
6. Attempting to convert an invalid string into a number.
7. and many more.

When such errors are encountered in a program, Java generates an error message and terminates the program abnormally. To handle these kinds of errors during the runtime, we use exception handling technique in java program.

Let’s take different kinds of example programs to understand better. In this program, we will divide an integer number by zero. Java compiler cannot detect it.

Program source code 5:

public class DivisionByZeroError
{	
public static void main(String[] args) 
{ 
 int a = 20, b = 5, c = 5;
 int z = a/(b-c); // Division by zero.
 
 System.out.println("Result: " +z);
  }
}

Output:
       Exception in thread "main" java.lang.ArithmeticException: / by zero
	at errorsProgram.DivisionByZeroError.main(DivisionByZeroError.java:8)

The above program is syntactically correct. There is no syntax error and therefore, does not cause any problem during compilation. While executing, runtime error occurred that is not detected by compiler.

The error is detected by JVM only in runtime. Default exception handler displays an error message and terminates the program abnormally without executing further statements in the program.

Let’s take an example program where we will try to retrieve a value from an array using an index that is out of range of the array.

Program source code 6: 

public class AccessingValueOutOfRangeError
{	
public static void main(String[ ] args) 
{ 
 int arr[ ] = {1, 2, 3, 4, 5}; // Here, array size is 5.
 System.out.println("Value at 5th position: "+arr[5]);
 }
}

Output:
       Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 5
	at errorsProgram.AccessingValueOutOfRangeError.main(AccessingValueOutOfRangeError.java:9)

Logical Errors in Java Program

Logical errors in Java are the most critical errors in a program and they are difficult to detect. These errors occur when the programmer uses incorrect logic or wrong formula in the coding.

The program will be compiled and executed successfully but does not return the expected output.

Logical errors are not detected either by Java compiler or JVM (Java runtime system). The programmer is entirely responsible for them. They can be detected by application testers when they compare the actual result with its expected result.

For example, a programmer wants to print even numbers from an array but he uses division (/) operator instead of modulus (%) operator to get the remainder of each number. Due to which he got the wrong results.

Let’s see the following source code related to this problem.

Program source code 7:

public class LogicalErrorEx
{	
public static void main(String[] args) 
{ 
 int a[]={1, 2 , 5, 6, 3, 10, 12, 13, 14};  
 
System.out.println("Even Numbers:");  
for(int i = 0; i <a.length; i++)
{  
if(a[i] / 2 == 0) // Using wrong operator.
{  
  System.out.println(a[i]);  
 }  
}  
 }
}

Output:
       Even Numbers:
       1

As you can see the program is successfully compiled and executed but the programmer got the wrong output due to logical errors in the program.

Seldom does a program run successfully at its first attempt. A software engineer in a company also commits several errors while designing the project or developing code.

These errors in a program are also called bugs and the process of fixing these bugs is called debugging.

All modern integrated development environments (IDEs) such as Eclipse, NetBeans, JBuilder, etc provide a tool known as debugger that helps to run the program step by step to detect bugs.

If you need professional help with Java homework assignments online, please address experts from AssignmentCore to get your Java projects done with no errors.

In this tutorial, we have familiarized different types of errors in java that may possibly occur in a program.
Thanks for reading!!!
Next ⇒ Exception handling Interview Programs for Practice

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While working with the programming languages like executing a software program, there are many instances that we run into issues due to the run time errors or compilation errors. All these errors occur when the application is running. You might come across an instance where the application acts differently in a negative way to the requirements, then it means that a runtime error took place.

As it is one of the most common type of error that occurs during a software executive, let us get a deep idea on how to fix common types of runtime errors in Java and also the steps to be taken to resolve them on a timely basis.

Fix the 5 Most Common Types of Runtime Errors in Java

 What is a Runtime Error in Java?

A runtime error in Java is referred to as an application error that comes up during the execution process of the program. This runtime error usually takes place when the syntax is corrected as expected while the issue lies during the program execution. All these errors can be detected by JVM – Java Virtual Machine and cannot be identified during the compilation time. Java is one of the most sought-after programming languages for the hiring managers across the world. So become an expert in Java through our Java Training and grab the best job opportunity.

Now, In this post, Let us discuss the top runtime errors in Java.

1. Division by zero errors
2.  IO errors
3. Out of range errors
4. Undefined object errors

Differences Between Compile Time Error and Runtime Error in Java

Compile time errors are those errors in which the syntax would be incorrect in the application code. An example would be like missing semicolons, parenthesis, incorrect keywords, usage of undeclared variables, etc. 

The Java compiler is capable of detecting the syntax errors during the compile time and the error message will be appearing on the screen. The compiler is also capable of preventing the code from the execution unless and until the error is resolved. Therefore it is important that these errors are addressed by making the necessary changes before the program is successfully executed.

The runtime errors occur during the program execution after the compilation has completed. Any program that is throwing a runtime error means that there are no issues with Syntax in the program.

Why Runtime Error Occurs in Java ?

 Below listed are the most common types of runtime errors that occur in Java.

1. Accessing an element that is out of range in an array
2. Dividing a number with 0
3. Less space or insufficient space memory
4. Conversion of an invalid string into a number
5. Attempting to store an incompatible value to a collection

When you come across such an address, you need to know that the Java compiler will be generating an error message and the program gets terminated abnormally. Runtime errors do not require to be caught explicitly. It is useful if you catch the runtime errors and resolve them to complete the program execution. 

Let us review a few of the most common runtime errors in Java programming with examples to gain a deeper understanding.

1. Accessing Out of Range Value in an Array

In the above example, the array is initialized with 8 elements. with the above code, An element at position number 8 is trying to get access and does not exist at all, leading to the Exception java.lang.ArrayIndexOutOfBoundsException:

Error :

2. Division by Zero Error

Below is an example of java.lang.ArithmeticException which occurs when the user is trying to code in such a way that they perform the division by zero.

In the above code, the integer num1 is getting to be divided by num2 which has a value of zero, which is leading to the exception called java.lang.ArithmeticException

Below is the Error Thrown :

3. Less Space or Insufficient Space Memory Error

Below is an example of java.lang.OutOfMemoryError, which occurs when the user is trying to initialize an Integer array with a very large size, and due to the Java heap being insufficient to allocate this memory space, it throws an Error  java.lang.OutOfMemoryError: Java heap space

Error :

4. Conversion of an Invalid string into a Number

Below is an example of java.lang.NumberFormatException, occurs when the user is trying to convert an alphanumeric string to an integer which leads to java.lang.NumberFormatException

Error :

5. Attempting to Store an Incompatible Value to a Collection

Below is an example where user has created the ArrayList of String but trying to store the integer value which leads to Exception   java.lang.Error: Unresolved compilation problem

Error :

How to solve Runtime Rrror in Java Programming?

 The runtime errors can be solved by using the try catch blocks in Java. Below are the steps to be followed:

1. You will need to Surround the statements that are capable of throwing an exception or a runtime error in the try catch blocks.
2. The next step is to catch the error.
3. Based on the requirements of the court or an application, it is important to take the necessary action.

Like we discussed earlier about the ArithmeticException example, it can be corrected by making the below changes.

As the code is surrounded in the try catch blocks, the program will continue to execute after the exception is encountered.

Result :

In this way, it is important for you to identify the Runtime errors and also clear them without any hesitation. You can make use of the try catch blocks and many other resolutions which were helped in successful program execution. Also you will be able to track, manage and analyze the errors in real time. So this was all from this tutorial about fixing the 5 most common types of Runtime Errors in Java But still, if you have any queries, feel free to ask in the comment section. And don’t forget to stay tuned with the Tutorials field to learn this type of awesome tutorial. HAPPY CODING.

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