Could not set unknown property 'mainClass' for extension 'application

Question

I'm using Gradle version 6.1 in my project.

The build.gradle for the project is given below:

plugins {
    id 'application'
}

application {
    mainClass = 'com.mytestproject.Main'
}

java {
    sourceCompatibility = JavaVersion.VERSION_1_8
    targetCompatibility = JavaVersion.VERSION_1_8
}

group 'com.mytestproject'
version '1.0-SNAPSHOT'

repositories {
    mavenCentral()
}

dependencies {
    testCompile group: 'junit', name: 'junit', version: '4.12'
}

But when I run this command ./gradlew assemble , it is giving me error given below:

./gradlew assemble

FAILURE: Build failed with an exception.

* Where:
Build file '/com/myproject/build.gradle' line: 6

* What went wrong:
A problem occurred evaluating root project 'JavaTestProject'.
> Could not set unknown property 'mainClass' for extension 'application' of type org.gradle.api.plugins.internal.DefaultJavaApplication.

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 484ms

Answer 1

Modify build.gradle to this:

apply plugin: "application"

mainClassName = "com.mytestproject.Main"

sourceCompatibility = 1.8
targetCompatibility = 1.8

group 'com.mytestproject'
version '1.0-SNAPSHOT'

repositories {
    mavenCentral()
}

dependencies {
    testCompile group: 'junit', name: 'junit', version: '4.12'
}

Run this commmand: ./gradlew build

Answer 2

You could try this (based off the source code ):

application {
    setMainClassName("some.package.Main")
}

Answer 3

There was a deprecation introduced in 6.4. It went from:

 application {
   mainClassName = "com.foo.bar.FooBar"
 }

To:

 application {
   mainClass.set("com.foo.bar.FooBar")
 }

The Docs:

https://docs.gradle.org/current/javadoc/org/gradle/api/plugins/JavaApplication.html#getMainClassName--