App

trait App extends DelayedInit

The App trait can be used to quickly turn objects into executable programs. Here is an example:

object Main extends App {
  Console.println("Hello World: " + (args mkString ", "))
}

No explicit main method is needed. Instead, the whole class body becomes the “main method”.

args returns the current command line arguments as an array.

Caveats

It should be noted that this trait is implemented using the DelayedInit functionality, which means that fields of the object will not have been initialized before the main method has been executed.

Future versions of this trait will no longer extend DelayedInit.

In Scala 3, the DelayedInit feature was dropped. App exists only in a limited form that also does not support command line arguments and will be deprecated in the future.

@main methods are the recommended scheme to generate programs that can be invoked from the command line in Scala 3.

@main def runMyProgram(args: String*): Unit = {
  // your program here
}

If programs need to cross-build between Scala 2 and Scala 3, it is recommended to use an explicit main method:

object Main {
  def main(args: Array[String]): Unit = {
    // your program here
  }
}

Annotations: @nowarn()
Source: App.scala

Linear Supertypes

DelayedInit, AnyRef, Any

Type Hierarchy

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Inherited

App
DelayedInit
AnyRef
Any

Implicitly

by any2stringadd
by StringFormat
by Ensuring
by ArrowAssoc

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Value Members

final def !=(arg0: Any): Boolean
Test two objects for inequality.
Test two objects for inequality.
returns
true if !(this == that), false otherwise.
Definition Classes
AnyRef → Any
final def ##: Int
Equivalent to x.hashCode except for boxed numeric types and null.
Equivalent to x.hashCode except for boxed numeric types and null. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For null returns a hashcode where null.hashCode throws a NullPointerException.
returns
a hash value consistent with ==
Definition Classes
AnyRef → Any
def +(other: String): String
Implicit
This member is added by an implicit conversion from App toany2stringadd[App] performed by method any2stringadd in scala.Predef.
Definition Classes
any2stringadd
def ->[B](y: B): (App, B)
Implicit
This member is added by an implicit conversion from App toArrowAssoc[App] performed by method ArrowAssoc in scala.Predef.
Definition Classes
ArrowAssoc
Annotations
@inline()
final def ==(arg0: Any): Boolean
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
returns
true if the receiver object is equivalent to the argument; false otherwise.
Definition Classes
AnyRef → Any
final def args: Array[String]
The command line arguments passed to the application's main method.
The command line arguments passed to the application's main method.
Attributes
protected
final def asInstanceOf[T0]: T0
Forces the compiler to treat the receiver object as having type T0, even though doing so may violate type safety.
Forces the compiler to treat the receiver object as having type T0, even though doing so may violate type safety.
This method is useful when you believe you have type information the compiler doesn't, and it also isn't possible to check the type at runtime. In such situations, skipping type safety is the only option.
It is platform dependent whether asInstanceOf has any effect at runtime. It might do a runtime type test on the erasure of T0, insert a conversion (such as boxing/unboxing), fill in a default value, or do nothing at all.
In particular, asInstanceOf is not a type test. It does **not** mean:
```
this match {
 case x: T0 => x
 case _     => throw ClassCastException("...")
```
Use pattern matching or isInstanceOf for type testing instead.
Situations where asInstanceOf is useful:
- when flow analysis fails to deduce T0 automatically
- when down-casting a type parameter or an abstract type member (which cannot be checked at runtime due to type erasure) If there is any doubt and you are able to type test instead, you should do so.
Be careful of using asInstanceOf when T0 is a primitive type. When T0 is primitive, asInstanceOf may insert a conversion instead of a type test. If your intent is to convert, use a toT method (x.toChar, x.toByte, etc.).
returns
the receiver object.
Definition Classes
Any
Exceptions thrown
ClassCastException if the receiver is not an instance of the erasure of T0, if that can be checked on this platform
def clone(): AnyRef
Create a copy of the receiver object.
Create a copy of the receiver object.
The default implementation of the clone method is platform dependent.
returns
a copy of the receiver object.
Attributes
protected[lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.CloneNotSupportedException]) @native()
Note
not specified by SLS as a member of AnyRef
def ensuring(cond: (App) => Boolean, msg: => Any): App
Implicit
This member is added by an implicit conversion from App toEnsuring[App] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: (App) => Boolean): App
Implicit
This member is added by an implicit conversion from App toEnsuring[App] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: Boolean, msg: => Any): App
Implicit
This member is added by an implicit conversion from App toEnsuring[App] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: Boolean): App
Implicit
This member is added by an implicit conversion from App toEnsuring[App] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
final def eq(arg0: AnyRef): Boolean
Tests whether the argument (that) is a reference to the receiver object (this).
Tests whether the argument (that) is a reference to the receiver object (this).
The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:
- It is consistent: for any non-null instances x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.
- For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false.
- null.eq(null) returns true.
When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).
returns
true if the argument is a reference to the receiver object; false otherwise.
Definition Classes
AnyRef
def equals(arg0: AnyRef): Boolean
The equality method for reference types.
The equality method for reference types. Default implementation delegates to eq.
See also equals in scala.Any.
returns
true if the receiver object is equivalent to the argument; false otherwise.
Definition Classes
AnyRef → Any
final val executionStart: Long
The time when the execution of this program started, in milliseconds since 1 January 1970 UTC.
def finalize(): Unit
Called by the garbage collector on the receiver object when there are no more references to the object.
Called by the garbage collector on the receiver object when there are no more references to the object.
The details of when and if the finalize method is invoked, as well as the interaction between finalize and non-local returns and exceptions, are all platform dependent.
Attributes
protected[lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.Throwable])
Note
not specified by SLS as a member of AnyRef
final def getClass(): Class[_ <: AnyRef]
Returns the runtime class representation of the object.
Returns the runtime class representation of the object.
returns
a class object corresponding to the runtime type of the receiver.
Definition Classes
AnyRef → Any
Annotations
@native()
def hashCode(): Int
The hashCode method for reference types.
The hashCode method for reference types. See hashCode in scala.Any.
returns
the hash code value for this object.
Definition Classes
AnyRef → Any
Annotations
@native()
final def isInstanceOf[T0]: Boolean
Test whether the dynamic type of the receiver object has the same erasure as T0.
Test whether the dynamic type of the receiver object has the same erasure as T0.
Depending on what T0 is, the test is done in one of the below ways:
- T0 is a non-parameterized class type, e.g. BigDecimal: this method returns true if the value of the receiver object is a BigDecimal or a subtype of BigDecimal.
- T0 is a parameterized class type, e.g. List[Int]: this method returns true if the value of the receiver object is some List[X] for any X. For example, List(1, 2, 3).isInstanceOf[List[String]] will return true.
- T0 is some singleton type x.type or literal x: this method returns this.eq(x). For example, x.isInstanceOf[1] is equivalent to x.eq(1)
- T0 is an intersection X with Y or X & Y: this method is equivalent to x.isInstanceOf[X] && x.isInstanceOf[Y]
- T0 is a union X | Y: this method is equivalent to x.isInstanceOf[X] || x.isInstanceOf[Y]
- T0 is a type parameter or an abstract type member: this method is equivalent to isInstanceOf[U] where U is T0's upper bound, Any if T0 is unbounded. For example, x.isInstanceOf[A] where A is an unbounded type parameter will return true for any value of x.
This is exactly equivalent to the type pattern _: T0
returns
true if the receiver object is an instance of erasure of type T0; false otherwise.
Definition Classes
Any
Note
due to the unexpectedness of List(1, 2, 3).isInstanceOf[List[String]] returning true and x.isInstanceOf[A] where A is a type parameter or abstract member returning true, these forms issue a warning.
final def main(args: Array[String]): Unit
The main method.
The main method. This stores all arguments so that they can be retrieved with args and then executes all initialization code segments in the order in which they were passed to delayedInit.
args
the arguments passed to the main method
final def ne(arg0: AnyRef): Boolean
Equivalent to !(this eq that).
Equivalent to !(this eq that).
returns
true if the argument is not a reference to the receiver object; false otherwise.
Definition Classes
AnyRef
final def notify(): Unit
Wakes up a single thread that is waiting on the receiver object's monitor.
Wakes up a single thread that is waiting on the receiver object's monitor.
Definition Classes
AnyRef
Annotations
@native()
Note
not specified by SLS as a member of AnyRef
final def notifyAll(): Unit
Wakes up all threads that are waiting on the receiver object's monitor.
Wakes up all threads that are waiting on the receiver object's monitor.
Definition Classes
AnyRef
Annotations
@native()
Note
not specified by SLS as a member of AnyRef
final def synchronized[T0](arg0: => T0): T0
Executes the code in body with an exclusive lock on this.
Executes the code in body with an exclusive lock on this.
returns
the result of body
Definition Classes
AnyRef
def toString(): String
Creates a String representation of this object.
Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.
returns
a String representation of the object.
Definition Classes
AnyRef → Any
final def wait(): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait--.
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait--.
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])
Note
not specified by SLS as a member of AnyRef
final def wait(arg0: Long, arg1: Int): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-int-
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-int-
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])
Note
not specified by SLS as a member of AnyRef
final def wait(arg0: Long): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-.
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-.
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException]) @native()
Note
not specified by SLS as a member of AnyRef

Deprecated Value Members

def delayedInit(body: => Unit): Unit
The init hook.
The init hook. This saves all initialization code for execution within main. This method is normally never called directly from user code. Instead it is called as compiler-generated code for those classes and objects (but not traits) that inherit from the DelayedInit trait and that do not themselves define a delayedInit method.
body
the initialization code to be stored for later execution
Definition Classes
App → DelayedInit
Annotations
@deprecated
Deprecated
(Since version 2.11.0) the delayedInit mechanism will disappear
def formatted(fmtstr: String): String
Returns string formatted according to given format string.
Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).
Implicit
This member is added by an implicit conversion from App toStringFormat[App] performed by method StringFormat in scala.Predef.
Definition Classes
StringFormat
Annotations
@deprecated @inline()
Deprecated
(Since version 2.12.16) Use formatString.format(value) instead of value.formatted(formatString), or use the f"" string interpolator. In Java 15 and later, formatted resolves to the new method in String which has reversed parameters.
def →[B](y: B): (App, B)
Implicit
This member is added by an implicit conversion from App toArrowAssoc[App] performed by method ArrowAssoc in scala.Predef.
Definition Classes
ArrowAssoc
Annotations
@deprecated
Deprecated
(Since version 2.13.0) Use -> instead. If you still wish to display it as one character, consider using a font with programming ligatures such as Fira Code.

Packages

Package structure

Automatic imports

Guide

Common Imports

Specifying Durations

Using Futures For Non-blocking Computation

Avoid Blocking

App

trait App extends DelayedInit

Caveats

Value Members

Deprecated Value Members

Inherited from DelayedInit

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion any2stringadd fromApp to any2stringadd[App]

Inherited by implicit conversion StringFormat fromApp to StringFormat[App]

Inherited by implicit conversion Ensuring fromApp to Ensuring[App]

Inherited by implicit conversion ArrowAssoc fromApp to ArrowAssoc[App]

Ungrouped

Packages

Package structure

Automatic imports

Guide

Common Imports

Specifying Durations

Using Futures For Non-blocking Computation

Avoid Blocking

App

trait App extends DelayedInit

Caveats

Value Members

Deprecated Value Members

Inherited from DelayedInit

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion any2stringadd fromApp to any2stringadd[App]

Inherited by implicit conversion StringFormat fromApp to StringFormat[App]

Inherited by implicit conversion Ensuring fromApp to Ensuring[App]

Inherited by implicit conversion ArrowAssoc fromApp to ArrowAssoc[App]

Ungrouped

App