Preconditions (Google App Engine API for Java)

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

      All Methods Static Methods Concrete Methods 
      Modifier and Type Method and Description
      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.
      static void checkState(boolean expression, java.lang.String errorMessage)
      Ensures the truth of an expression involving the state of the calling instance.
      static void checkState(boolean expression, java.lang.String errorMessageTemplate, java.lang.Object... errorMessageArgs)
      Ensures the truth of an expression involving the state of the calling instance.
      • 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) if not null (a null will not be converted).
        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 using String.format(String, Object...). if not null (a null will not be converted).
        errorMessageArgs - the arguments to be substituted into the message template.
        Throws:
        java.lang.IllegalArgumentException - if expression is false
      • 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
      • checkState

        public static void checkState(boolean expression,
                                      java.lang.String errorMessageTemplate,
                                      java.lang.Object... errorMessageArgs)
        Ensures the truth of an expression involving the state of the calling instance.
        Parameters:
        expression - a boolean expression
        errorMessageTemplate - a template for the exception message should the check fail. The message is formed using String.format(String, Object...). if not null (a null will not be converted).
        errorMessageArgs - the arguments to be substituted into the message template.
        Throws:
        java.lang.IllegalStateException - if expression is false
      • checkState

        public static void checkState(boolean expression,
                                      java.lang.String errorMessage)
        Ensures the truth of an expression involving the state of the calling instance.
        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) if not null (a null will not be converted).
        Throws:
        java.lang.IllegalStateException - if expression is false

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