Android项目编译和运行时没有模块级build.gradle。对吗?

文件如下所示:

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.2.3'
    }
}
apply plugin: 'com.android.application'

dependencies {
    compile fileTree(dir: 'libs', include: '*.jar')
}

android {
    compileSdkVersion 21
    buildToolsVersion "22.0.1"

    productFlavors {
        arm {
            ndk {
                abiFilters = ["armeabi-v7a", "arm64-v8a"]
            }
        }
    }

    defaultConfig {
        applicationId "com.mycompany.myapp"
        minSdkVersion 17
        targetSdkVersion 19
        versionCode 1
        versionName "9.99.99.99"
    }

    signingConfigs {
        release {
            storeFile file("myapp.jks")
            storePassword "mypwd"
            keyAlias "myalias"
            keyPassword "mykeypwd"
        }
    }

    buildTypes {
        release {
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
            signingConfig signingConfigs.release
        }
        debug{
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
            signingConfig signingConfigs.release
        }
    }

    sourceSets {
        main {
            manifest.srcFile 'AndroidManifest.xml'
            java.srcDirs = ['src']
            resources.srcDirs = ['src']
            aidl.srcDirs = ['src']
            renderscript.srcDirs = ['src']
            res.srcDirs = ['res']
            assets.srcDirs = ['assets']
            jniLibs.srcDirs = ['libs']
        }

        // Move the tests to tests/java, tests/res, etc...
        instrumentTest.setRoot('tests')

        // Move the build types to build-types/<type>
        // For instance, build-types/debug/java, build-types/debug/AndroidManifest.xml, ...
        // This moves them out of them default location under src/<type>/... which would
        // conflict with src/ being used by the main source set.
        // Adding new build types or product flavors should be accompanied
        // by a similar customization.
        debug.setRoot('build-types/debug')
        release.setRoot('build-types/release')
    }
}

我读过的所有文档和教程,包括Google和Gradle官方文档,都说明应该有两个Gradle文件,项目级和模块级。

如果项目只有一个模块,那么必须使用模块级build.gradle吗?