解释 java.lang.NoSuchMethodError 消息

我得到了下面的运行时错误消息(以及堆栈跟踪的第一行，它指向第94行)。我想知道为什么没有这种方法。

java.lang.NoSuchMethodError:
com.sun.tools.doclets.formats.html.SubWriterHolderWriter.printDocLinkForMenu(
ILcom/sun/javadoc/ClassDoc;Lcom/sun/javadoc/MemberDoc;
Ljava/lang/String;Z)Ljava/lang/String;
at com.sun.tools.doclets.formats.html.AbstractExecutableMemberWriter.writeSummaryLink(
AbstractExecutableMemberWriter.java:94)

WriteSummaryLink 的第94行如下所示。

问题
“ ILcom”或者“ Z”是什么意思？
为什么括号里有四种类型 (ILcom/sun/javadoc/ClassDoc; Lcom/sun/javadoc/MemberDoc; Ljava/lang/String; Z) 括号后面还有一个 Ljava/lang/String; 当 printDocLinkForMenu 方法明显有五个参数的时候？

代码细节
WriteSummaryLink 方法是:

protected void writeSummaryLink(int context, ClassDoc cd, ProgramElementDoc member) {
ExecutableMemberDoc emd = (ExecutableMemberDoc)member;
String name = emd.name();
writer.strong();
writer.printDocLinkForMenu(context, cd, (MemberDoc) emd, name, false);  // 94
writer.strongEnd();
writer.displayLength = name.length();
writeParameters(emd, false);
}

下面是第94行调用的方法:

public void printDocLinkForMenu(int context, ClassDoc classDoc, MemberDoc doc,
String label, boolean strong) {
String docLink = getDocLink(context, classDoc, doc, label, strong);
print(deleteParameterAnchors(docLink));
}

77149

小开

What does "ILcom" or "Z" mean?

Those are mapping types for native types. You can find an overview here.

Native Type    | Java Language Type | Description      | Type signature
---------------+--------------------+------------------+----------------
unsigned char  | jboolean           | unsigned 8 bits  | Z
signed char    | jbyte              | signed 8 bits    | B
unsigned short | jchar              | unsigned 16 bits | C
short          | jshort             | signed 16 bits   | S
long           | jint               | signed 32 bits   | I
long long      | jlong              | signed 64 bits   | J
__int64        |                    |                  |
float          | jfloat             | 32 bits          | F
double         | jdouble            | 64 bits          | D

In addition, the signature "L fully-qualified-class ;" would mean the class uniquely specified by that name; e.g., the signature "Ljava/lang/String;" refers to the class java.lang.String. Also, prefixing [ to the signature makes the array of that type; for example, [I means the int array type.

As to your next question:

Why there are four types in parentheses (ILcom/sun/javadoc/ClassDoc;Lcom/sun/javadoc/MemberDoc;Ljava/lang/String;Z) and one after the parentheses Ljava/lang/String; when the method printDocLinkForMenu clearly has five parameters?

Because you're not running the code you think you're running. The actually running code is trying to call exactly that method described in the error message, with actually five parameters (the I should be counted separately) and a String return type, but this method doesn't exist in the runtime classpath (while it was available in the compiletime classpath), hence this error. Also see the NoSuchMethodError javadoc:

Thrown if an application tries to call a specified method of a class (either static or instance), and that class no longer has a definition of that method.

Normally, this error is caught by the compiler; this error can only occur at run time if the definition of a class has incompatibly changed.

So, verify if you're actually running the right version of the code as you've posted in your question and are using the right dependencies in the runtime classpath and not having duplicate different versioned libraries in the classpath.

Update: the exception signifies that the actual code is (implicitly) trying to use the method like as follows:

String s = printDocLinkForMenu(context, cd, (MemberDoc) emd, name, false);

Because it is expecting a String outcome while it is declared void.

Character Type Interpretation ------------------------------------------ B byte signed byte C char Unicode character D double double-precision floating-point value F float single-precision floating-point value I int integer J long long integer L<classname>; reference an instance of class S short signed short Z boolean true or false [ reference one array dimension

From section 4.3.2 of the JVM Spec:

From section 4.3.3, Method descriptors:

A method descriptor represents the parameters that the method takes and the value that it returns:

MethodDescriptor:
( ParameterDescriptor* ) ReturnDescriptor

Thus,

(ILcom/sun/javadoc/ClassDoc;Lcom/sun/javadoc/MemberDoc;Ljava/lang/String;Z) Ljava/lang/String;

translates to:

A method with int, ClassDoc, MemberDoc, String and boolean as parameters, and which returns a String. Note that only reference parameters are separated with a semicolon, since the semicolon is part of their character representation.

So, to sum up:

There are five parameters (int, ClassDoc, MemberDoc, String, boolean) and one return type (String).