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

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

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

Answer 2

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 3

Actually just modifying the application block to

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

does the same thing.

The problem seems to be that there used to be a mainClass attribute on the org.gradle.api.plugins.internal.DefaultJavaApplication class, but it later got renamed to mainClassName, rendering previous tutorials invalid.