com.google.appengine.api.search.checkers
Class Preconditions

java.lang.Object
  com.google.appengine.api.search.checkers.Preconditions

public final class Preconditions
extends java.lang.Object

Simple static methods to be called at the start of your own methods to verify correct arguments and state. This allows constructs such as

     if (count <= 0) {
       throw new IllegalArgumentException("must be positive: " + count);
     }

to be replaced with the more compact

     checkArgument(count > 0, "must be positive: %s", count);

Note that the sense of the expression is inverted; with Preconditions you declare what you expect to be true, just as you do with an assert or a JUnit assertTrue call.

Method Summary

static void	checkArgument(boolean expression, java.lang.Object errorMessage) Ensures the truth of an expression involving one or more parameters to the calling method.
static void	checkArgument(boolean expression, java.lang.String errorMessageTemplate, java.lang.Object... errorMessageArgs) Ensures the truth of an expression involving one or more parameters to the calling method.
static <T> T	checkNotNull(T reference, java.lang.Object errorMessage) Ensures that an object reference passed as a parameter to the calling method is not null.

Methods inherited from class java.lang.Object

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

Method Detail

checkArgument

public static void checkArgument(boolean expression,
                                 java.lang.Object errorMessage)

Ensures the truth of an expression involving one or more parameters to the calling method.

Parameters:

expression - a boolean expression

errorMessage - the exception message to use if the check fails; will be converted to a string using String.valueOf(Object)

Throws:

java.lang.IllegalArgumentException - if expression is false

checkArgument

public static void checkArgument(boolean expression,
                                 java.lang.String errorMessageTemplate,
                                 java.lang.Object... errorMessageArgs)

Ensures the truth of an expression involving one or more parameters to the calling method.

Parameters:

expression - a boolean expression

errorMessageTemplate - a template for the exception message should the check fail. The message is formed by replacing each %s place-holder in the template with an argument. These are matched by position - the first %s gets errorMessageArgs[0], etc. Unmatched arguments will be appended to the formatted message in square braces. Unmatched place-holders will be left as-is

errorMessageArgs - the arguments to be substituted into the message template. Arguments are converted to strings using String.valueOf(Object)

Throws:

java.lang.IllegalArgumentException - if expression is false

java.lang.NullPointerException - if the check fails and either errorMessageTemplate or errorMessageArgs is null (don't let this happen)

checkNotNull

public static <T> T checkNotNull(T reference,
                                 java.lang.Object errorMessage)

Ensures that an object reference passed as a parameter to the calling method is not null.

Parameters:

reference - an object reference

errorMessage - the exception message to use if the check fails; will be converted to a string using String.valueOf(Object)

Returns:

the non-null reference that was validated

Throws:

java.lang.NullPointerException - if reference is null