org.yarnandtail.andhow.property

Class FlagProp

java.lang.Object

org.yarnandtail.andhow.property.PropertyBase<Boolean>

org.yarnandtail.andhow.property.FlagProp

All Implemented Interfaces:

Property<Boolean>

public class FlagProp
extends PropertyBase<Boolean>

A True/False switch that is never null and behaves similarly to a 'nix cmd line switch.

This would be used for command line arguments that are true by being presence, e.g.:
java MyClass launch
If launch is the name or alias of a FlagProp, launch will true by its presence, without requiring launch=true (although that will also work).

NOTE: The behavior of this class may be changing
The existing behavior causes unexpected values in properties files and will likely change in the 0.5.0 release so that it behaves like a BolProp everywhere except on command line.

If unspecified, a Flag defaults to false, however, the default can be set to true (but not to null).

A FlagProp is similar to a BolProp, but with these differences:

• A Flag is never null - it will always return true or false. Thus, A FlagProp will never throw a RequirementProblem error during configuration - it always has a value.
• FlagProp.getDefaultValue() never returns null and defaults to false. Via the constructor or builder, it is possible to set the default to be true. In that case a loader would need to find it explicitly set to false to change its value, e.g. propertyName=false.
• Currently (prior to 0.5.0), referencing a FlagProp in any configuration source (not just command line args) will set it to true. For instance, a 'launch' flag will be set true simply by including:
  launch =
  in a properties file. That will likely change in the 0.5.0 release (see note above).

The technical details

When the name refering to a FlagProp is found, the value is first trimmed by the TrimToNullTrimmer, which removes all whitespace and ultimately turns the value into null if the value is all whitespace. Since simply being present counts as 'true' for a flag, finding a null value sets the Flag to true.

If after trimming the value is not null, it is parsed by TextUtil.toBoolean(java.lang.String) to determine if the String is considered true or false.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	FlagProp.FlagBuilder

Constructor Summary

Constructors

Constructor and Description
FlagProp(Boolean defaultValue, String shortDesc, List<Name> aliases, PropertyType paramType, ValueType<Boolean> valueType, Trimmer trimmer, String helpText)

Method Summary

Modifier and Type	Method and Description
static FlagProp.FlagBuilder	builder() A chainable builder for this property that should terminate with build()
Boolean	getValue() Returns the effective value of this property.

Methods inherited from class org.yarnandtail.andhow.property.PropertyBase

getDefaultValue, getDescription, getExplicitValue, getHelpText, getPropertyType, getRequestedAliases, getTrimmer, getValidators, getValueType, isNonNullRequired

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.yarnandtail.andhow.api.Property

getCanonicalName, getInAliases, getOutAliases, getValueAsString, isExplicitlySet

Constructor Detail

FlagProp

public FlagProp(Boolean defaultValue,
                String shortDesc,
                List<Name> aliases,
                PropertyType paramType,
                ValueType<Boolean> valueType,
                Trimmer trimmer,
                String helpText)

Method Detail

getValue

public Boolean getValue()

Description copied from interface: Property

Returns the effective value of this property. The effective value is the explicitly configured value, or if that is null, the default value. Explicitly setting a property to null is not possible because it will just be ignored and the default used instead.

Specified by:

getValue in interface Property<Boolean>

Overrides:

getValue in class PropertyBase<Boolean>

Returns:

May be null, unless the property is marked as required.

builder

public static FlagProp.FlagBuilder builder()

A chainable builder for this property that should terminate with build()

Use as FlagProp.builder()...series of builder methods...build();

Returns:

The builder instance that can be chained