Syntax Checking in Java [closed]

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I am currently working on a program that has an embedded text editor. The users are supposed to type java code in the editor. The code typed into the editor is then made into a string. I just want something that would check for missing parenthesis or a try without a catch, etc. It doesn't need to be compiled. I've looked around quite a bit, but I'm still new to programming and can't implement some of the harder stuff.

So to make it shorter: I'm looking for some java package that will analyze code for syntax errors.

Answer 1

As of Java 6 you can use JavaCompiler to compile the text and get back Diagnostic objects that tell you what problems the file has (if any). So for your example you'd need to take the content of the editor and pass it to the JavaCompiler, run it, and report back any problems. Example that follows assumes editor text written out to a file.

Example code:

File to Check

public class HelloBuggyWorld {
    String test // missing a semicolon

    public static void main (String [] args) {
        System.out.println('Hello World!');  // should be double quoted
    }
}

Checker

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Formatter;
import java.util.List;
import java.util.Locale;

import javax.tools.Diagnostic;
import javax.tools.DiagnosticCollector;
import javax.tools.JavaCompiler;
import javax.tools.JavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;

public class JavaSyntaxChecker {
    public static void main(String[] args) {
        System.out.println(JavaSyntaxChecker.check("/path/to/HelloBuggyWorld.java"));
    }

    public static List<String> check(String file) {
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

        StandardJavaFileManager fileManager = compiler.getStandardFileManager(null, null, null);
        Iterable<? extends JavaFileObject> compilationUnits =
                fileManager.getJavaFileObjectsFromStrings(Arrays.asList(file));

        DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>();
        compiler.getTask(null, fileManager, diagnostics, null, null, compilationUnits).call();

        List<String> messages = new ArrayList<String>();
        Formatter formatter = new Formatter();
        for (Diagnostic diagnostic : diagnostics.getDiagnostics()) {
            messages.add(diagnostic.getKind() + ":\t Line [" + diagnostic.getLineNumber() + "] \t Position [" + diagnostic.getPosition() + "]\t" + diagnostic.getMessage(Locale.ROOT) + "\n");
        }

        return messages;
    }
}

Output

From running the main method.

[ERROR:  Line [5]    Position [124] HelloBuggyWorld.java:5: unclosed character literal
, ERROR:     Line [5]    Position [126] HelloBuggyWorld.java:5: ';' expected
, ERROR:     Line [5]    Position [131] HelloBuggyWorld.java:5: not a statement
, ERROR:     Line [5]    Position [136] HelloBuggyWorld.java:5: ';' expected
, ERROR:     Line [5]    Position [137] HelloBuggyWorld.java:5: unclosed character literal
]

Answer 2

You can look at Beanshell interpreter. It can interpret Java code (both full source file and code fragments) and report errors on syntax.

Answer 3

Assuming that you want to validate that user has input java code with correct syntax then you could invoke javac compiler directly from within your program.

public int com.sun.tools.javac.Main.compile(String[] args);

You need tools.jar in your class path.

Answer 4

You can use JDT to parse and analyze source.

That's scala example. It's easy to do the same with java:

val str = "..." // Checking source code
val parser : ASTParser = ASTParser.newParser(org.eclipse.jdt.core.dom.AST.JLS3)    
val options = JavaCore.getOptions.asInstanceOf[java.util.Map[Object, Object]]
options.put(JavaCore.COMPILER_COMPLIANCE, JavaCore.VERSION_1_7)
options.put(JavaCore.COMPILER_CODEGEN_TARGET_PLATFORM, JavaCore.VERSION_1_7)
options.put(JavaCore.COMPILER_SOURCE, JavaCore.VERSION_1_7)
parser.setCompilerOptions(options)
parser.setSource(str.toCharArray)
val cu: CompilationUnit = parser.createAST(null).asInstanceOf[CompilationUnit]

CompilationUnit has method getProblems(). It returns list of detailed problem reports.

Answer 5

you can probably embed the eclipse syntax checker into your program.

Answer 6

This is pretty standard in Eclipse and Netbeans.

If you want a nice, simple editor with parentheses-checks I'd vote for Sublime text.

Answer 7

I suggest 1) CheckSyntax, "a development tool to help programmers write Java code that adheres to a coding standard." It has many standard checks, and 2) FindBugs, "a program which uses static analysis to look for bugs in Java code."