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 unix cmd line switch. If unspecified, a Flag defaults to false, however, the default can be set to true (but not null). Best used for on/off flags, particularly if used from command line where a null value makes no sense. 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.isNonNullRequired() always returns true, as if mustNotBeNull() was called on the builder.
• 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.
• Loaders will interpret the presence of the flag as setting the flag to True (where possible). For instance, if a Flag is aliased as -enableTorpedos, including -enableTorpedos as a command line argument will cause the CmdLineLoader to set it to true.

The technical details

What a value is assigned to a FlagProp, it 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 'on' 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.

Author:

eeverman

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()
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

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()