{"id":59778,"date":"2020-08-19T06:20:24","date_gmt":"2020-08-19T06:20:24","guid":{"rendered":"https:\/\/www.baeldung.com\/?p=85956"},"modified":"2020-08-19T06:20:24","modified_gmt":"2020-08-19T06:20:24","slug":"nosuchmethoderror-in-java","status":"publish","type":"post","link":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/2020\/08\/19\/nosuchmethoderror-in-java\/","title":{"rendered":"NoSuchMethodError in Java"},"content":{"rendered":"

<\/p>\n

1. Overview<\/h2>\n
<\/div>\n

In this tutorial, we’ll look at the java.lang.NoSuchMethodError <\/em>and some ways to handle it.<\/p>\n

2. NoSuchMethodError<\/em><\/h2>\n
<\/div>\n

As the name suggests, the NoSuchMethodError<\/em> occurs when a particular method is not found<\/strong>. This method can either be an instance method or a static method.<\/p>\n

In most cases,<\/strong> we’re able to catch this error at compile-time. Hence<\/strong>, it’s not a big issue. However, sometimes it could be thrown at runtime<\/strong>, then finding it becomes a bit difficult. According to the Oracle documentation<\/a>, this error may occur at runtime if a class has been incompatibly changed.<\/p>\n

Hence, we may encounter this error in the following cases. Firstly, if we do just a partial recompilation<\/strong> of our code.\u00a0Secondly, if there is version incompatibility with the dependencies<\/strong> in our application, such as the external jars.<\/p>\n

Note that the NoSuchMethodError<\/em> inheritance tree includes\u00a0IncompatibleClassChangeError<\/a>\u00a0and\u00a0LinkageError<\/a>.<\/em> These errors are associated with an\u00a0incompatible class change after compilation.<\/p>\n

3. Example of NoSuchMethodError<\/em><\/h2>\n
<\/div>\n

Let\u2019s see this error in action with an example. For this, we’ll create two classes. First is SpecialToday <\/em>which will list the specials for the day in a restaurant:\u00a0
\n
\n<\/em><\/p>\n

public class SpecialToday {\r\n    private static String desert = \"Chocolate Cake\";\r\n    public static String getDesert() {\r\n        return desert;\r\n    }\r\n}<\/code><\/pre>\n
The second class MainMenu<\/em> calls methods from SpecialsToday:
\n
\n<\/em><\/p>\n
public class MainMenu {\r\n    public static void main(String[] args) {\r\n        System.out.println(\"Today's Specials: \" + getSpecials());\r\n    }\r\n    public static String getSpecials() {\r\n        return SpecialToday.getDesert();\r\n    }\r\n}<\/code><\/pre>\n
Here the output will be:<\/p>\n
Today's Specials: Chocolate Cake<\/code><\/pre>\n
Next, we\u2019ll delete the method getDesert() in SpecialToday <\/em>and recompile only this updated class. This time when we run our MainMenu, <\/em>we notice the following runtime error:<\/p>\n
Exception in thread \"main\" java.lang.NoSuchMethodError: SpecialToday.getDesert()Ljava\/lang\/String;<\/code><\/pre>\n
4. How to Handle NoSuchMethodError<\/em><\/h2>\n
<\/div>\n
Now let’s see how we can handle this. For the above code, let\u2019s do a full clean-compile,<\/strong>\u00a0including both the classes. We’ll notice that the error will be caught while we’re compiling. If we use an IDE like Eclipse<\/strong>, it will be detected even earlier,<\/strong> as soon as we update SpecialsToday<\/em>.<\/p>\n
Hence if we run into this error with our applications, as a first step, we’ll do a full clean compile. With maven, we’ll run the mvn clean install <\/em>command.<\/p>\n
Sometimes the issue is with the external dependencies of our application. In this case, we’ll first check the order of the jars<\/strong> in the build path pulled by the classpath loader. And we’ll trace and update the inconsistent jar.<\/p>\n
However, if we still encounter this error at runtime, we’ll have to dig deeper. We’ll have to ensure that the Compile-time and the Runtime classes and jars have the same versions<\/strong>. For this, we can run the application with -verbose: class option <\/strong>to check the loaded classes. We can run the command as follows:<\/p>\n
$ java -verbose:class com.baeldung.exceptions.nosuchmethoderror.MainMenu\r\n[0.014s][info][class,load] opened: \/usr\/lib\/jvm\/java-11-openjdk-amd64\/lib\/modules\r\n[0.015s][info][class,load] opened: \/usr\/share\/java\/java-atk-wrapper.jar\r\n[0.028s][info][class,load] java.lang.Object source: shared objects file\r\n[0.028s][info][class,load] java.io.Serializable source: shared objects file<\/code><\/pre>\n
Using this information about all the classes being loaded in the individual jars, during runtime, we can trace the incompatible dependency.<\/p>\n
We should also make sure that there are no duplicate classes<\/strong> in two or more jars. In most cases, maven will help control conflicting dependencies<\/strong> directly. Furthermore, we can run the mvn dependency: tree<\/em> command to get the dependency tree of our project as follows:<\/p>\n
$ mvn dependency:tree\r\n[INFO] Scanning for projects...\r\n[INFO]\r\n[INFO] -------------< com.baeldung.exceptions:nosuchmethoderror >--------------\r\n[INFO] Building nosuchmethoderror 0.0.1-SNAPSHOT\r\n[INFO] --------------------------------[ jar ]---------------------------------\r\n[INFO]\r\n[INFO] --- maven-dependency-plugin:2.8:tree (default-cli) @ nosuchmethoderror ---\r\n[INFO] com.baeldung.exceptions:nosuchmethoderror:jar:0.0.1-SNAPSHOT\r\n[INFO] \\- org.junit:junit-bom:pom:5.7.0-M1:compile<\/code><\/pre>\n
We can check the libraries and their versions in the list generated by this command. Moreover, we can also manage dependencies using maven tags. Using the <exclusions><\/em> tag<\/a>, we can exclude the problematic dependency. Using the <optional><\/em> tag<\/a>, we can prevent unwanted dependencies from being bundled in the jar or war.<\/p>\n
5. Conclusion<\/h2>\n
<\/div>\n
In this article, we addressed NoSuchMethodError<\/em>. We discussed the cause of this error and also ways to handle it. For more details on how to handle errors properly, please refer to our article on catching Java errors<\/a>.<\/p>\n
As always, the code presented in this article is available over on GitHub.<\/a><\/p>\n
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Let’s look at the java.lang.NoSuchMethodError and some ways to handle it.<\/p>\n
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