2.1/dev/core/src/com/google/gwt/dev/util/Preconditions.java - gwt - Git at Google

 /*
  * Copyright 2009 Google Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not
  * use this file except in compliance with the License. You may obtain a copy of
  * the License at
  *
  * http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  * License for the specific language governing permissions and limitations under
  * the License.
  */
 package com.google.gwt.dev.util;

 /**
  * Simple static methods to be called at the start of your own methods to verify
  * correct arguments and state. This allows constructs such as
  * <pre>
  *     if (count <= 0) {
  *       throw new IllegalArgumentException("must be positive: " + count);
  *     }</pre>
  *
  * to be replaced with the more compact
  * <pre>
  *     checkArgument(count > 0, "must be positive: %s", count);</pre>
  *
  * Note that the sense of the expression is inverted; with {@code Preconditions}
  * you declare what you expect to be <i>true</i>, just as you do with an
  * <a href="http://java.sun.com/j2se/1.5.0/docs/guide/language/assert.html">
  * {@code assert}</a> or a JUnit {@code assertTrue} call.
  *
  * <p><b>Warning:</b> only the {@code "%s"} specifier is recognized as a
  * placeholder in these messages, not the full range of {@link
  * String#format(String, Object[])} specifiers.
  *
  * <p>Take care not to confuse precondition checking with other similar types
  * of checks! Precondition exceptions -- including those provided here, but also
  * {@link IndexOutOfBoundsException}, {@link
  * UnsupportedOperationException} and others -- are used to signal that the
  * <i>calling method</i> has made an error. This tells the caller that it should
  * not have invoked the method when it did, with the arguments it did, or
  * perhaps ever. Postcondition or other invariant failures should not throw
  * these types of exceptions.
  *
  * <p>This class was adapted from google-collections project.
  */
 public final class Preconditions {
   /**
    * Ensures the truth of an expression involving one or more parameters to the
    * calling method.
    *
    * @param expression a boolean expression
    * @throws IllegalArgumentException if {@code expression} is false
    */
   public static void checkArgument(boolean expression) {
     if (!expression) {
       throw new IllegalArgumentException();
     }
   }

   /**
    * Ensures the truth of an expression involving one or more parameters to the
    * calling method.
    *
    * @param expression a boolean expression
    * @param errorMessage the exception message to use if the check fails; will
    *     be converted to a string using {@link String#valueOf(Object)}
    * @throws IllegalArgumentException if {@code expression} is false
    */
   public static void checkArgument(boolean expression, Object errorMessage) {
     if (!expression) {
       throw new IllegalArgumentException(String.valueOf(errorMessage));
     }
   }

   /**
    * Ensures the truth of an expression involving one or more parameters to the
    * calling method.
    *
    * @param expression a boolean expression
    * @param errorMessageTemplate a template for the exception message should the
    *     check fail. The message is formed by replacing each {@code %s}
    *     placeholder in the template with an argument. These are matched by
    *     position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
    *     Unmatched arguments will be appended to the formatted message in square
    *     braces. Unmatched placeholders will be left as-is.
    * @param errorMessageArgs the arguments to be substituted into the message
    *     template. Arguments are converted to strings using
    *     {@link String#valueOf(Object)}.
    * @throws IllegalArgumentException if {@code expression} is false
    * @throws NullPointerException if the check fails and either {@code
    *     errorMessageTemplate} or {@code errorMessageArgs} is null (don't let
    *     this happen)
    */
   public static void checkArgument(boolean expression,
       String errorMessageTemplate, Object... errorMessageArgs) {
     if (!expression) {
       throw new IllegalArgumentException(
           format(errorMessageTemplate, errorMessageArgs));
     }
   }

   /**
    * Ensures that {@code index} specifies a valid <i>element</i> in an array,
    * list or string of size {@code size}. An element index may range from zero,
    * inclusive, to {@code size}, exclusive.
    *
    * @param index a user-supplied index identifying an element of an array, list
    *     or string
    * @param size the size of that array, list or string
    * @return the value of {@code index}
    * @throws IndexOutOfBoundsException if {@code index} is negative or is not
    *     less than {@code size}
    * @throws IllegalArgumentException if {@code size} is negative
    */
   public static int checkElementIndex(int index, int size) {
     return checkElementIndex(index, size, "index");
   }

   /**
    * Ensures that {@code index} specifies a valid <i>element</i> in an array,
    * list or string of size {@code size}. An element index may range from zero,
    * inclusive, to {@code size}, exclusive.
    *
    * @param index a user-supplied index identifying an element of an array, list
    *     or string
    * @param size the size of that array, list or string
    * @param desc the text to use to describe this index in an error message
    * @return the value of {@code index}
    * @throws IndexOutOfBoundsException if {@code index} is negative or is not
    *     less than {@code size}
    * @throws IllegalArgumentException if {@code size} is negative
    */
   public static int checkElementIndex(int index, int size, String desc) {
     // Carefully optimized for execution by hotspot (explanatory comment above)
     if (index < 0 || index >= size) {
       throw new IndexOutOfBoundsException(badElementIndex(index, size, desc));
     }
     return index;
   }

   /**
    * Ensures that an object reference passed as a parameter to the calling
    * method is not null.
    *
    * @param reference an object reference
    * @return the non-null reference that was validated
    * @throws NullPointerException if {@code reference} is null
    */
   public static <T> T checkNotNull(T reference) {
     if (reference == null) {
       throw new NullPointerException();
     }
     return reference;
   }

   /**
    * Ensures that an object reference passed as a parameter to the calling
    * method is not null.
    *
    * @param reference an object reference
    * @param errorMessage the exception message to use if the check fails; will
    *     be converted to a string using {@link String#valueOf(Object)}
    * @return the non-null reference that was validated
    * @throws NullPointerException if {@code reference} is null
    */
   public static <T> T checkNotNull(T reference, Object errorMessage) {
     if (reference == null) {
       throw new NullPointerException(String.valueOf(errorMessage));
     }
     return reference;
   }

   /**
    * Ensures that an object reference passed as a parameter to the calling
    * method is not null.
    *
    * @param reference an object reference
    * @param errorMessageTemplate a template for the exception message should the
    *     check fail. The message is formed by replacing each {@code %s}
    *     placeholder in the template with an argument. These are matched by
    *     position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
    *     Unmatched arguments will be appended to the formatted message in square
    *     braces. Unmatched placeholders will be left as-is.
    * @param errorMessageArgs the arguments to be substituted into the message
    *     template. Arguments are converted to strings using
    *     {@link String#valueOf(Object)}.
    * @return the non-null reference that was validated
    * @throws NullPointerException if {@code reference} is null
    */
   public static <T> T checkNotNull(T reference, String errorMessageTemplate,
       Object... errorMessageArgs) {
     if (reference == null) {
       // If either of these parameters is null, the right thing happens anyway
       throw new NullPointerException(
           format(errorMessageTemplate, errorMessageArgs));
     }
     return reference;
   }

   /**
    * Ensures that {@code index} specifies a valid <i>position</i> in an array,
    * list or string of size {@code size}. A position index may range from zero
    * to {@code size}, inclusive.
    *
    * @param index a user-supplied index identifying a position in an array, list
    *     or string
    * @param size the size of that array, list or string
    * @return the value of {@code index}
    * @throws IndexOutOfBoundsException if {@code index} is negative or is
    *     greater than {@code size}
    * @throws IllegalArgumentException if {@code size} is negative
    */
   public static int checkPositionIndex(int index, int size) {
     return checkPositionIndex(index, size, "index");
   }

   /**
    * Ensures that {@code index} specifies a valid <i>position</i> in an array,
    * list or string of size {@code size}. A position index may range from zero
    * to {@code size}, inclusive.
    *
    * @param index a user-supplied index identifying a position in an array, list
    *     or string
    * @param size the size of that array, list or string
    * @param desc the text to use to describe this index in an error message
    * @return the value of {@code index}
    * @throws IndexOutOfBoundsException if {@code index} is negative or is
    *     greater than {@code size}
    * @throws IllegalArgumentException if {@code size} is negative
    */
   public static int checkPositionIndex(int index, int size, String desc) {
     // Carefully optimized for execution by hotspot (explanatory comment above)
     if (index < 0 || index > size) {
       throw new IndexOutOfBoundsException(badPositionIndex(index, size, desc));
     }
     return index;
   }

   /**
    * Ensures that {@code start} and {@code end} specify a valid <i>positions</i>
    * in an array, list or string of size {@code size}, and are in order. A
    * position index may range from zero to {@code size}, inclusive.
    *
    * @param start a user-supplied index identifying a starting position in an
    *     array, list or string
    * @param end a user-supplied index identifying a ending position in an array,
    *     list or string
    * @param size the size of that array, list or string
    * @throws IndexOutOfBoundsException if either index is negative or is
    *     greater than {@code size}, or if {@code end} is less than {@code start}
    * @throws IllegalArgumentException if {@code size} is negative
    */
   public static void checkPositionIndexes(int start, int end, int size) {
     // Carefully optimized for execution by hotspot (explanatory comment above)
     if (start < 0 || end < start || end > size) {
       throw new IndexOutOfBoundsException(badPositionIndexes(start, end, size));
     }
   }

   /**
    * Ensures the truth of an expression involving the state of the calling
    * instance, but not involving any parameters to the calling method.
    *
    * @param expression a boolean expression
    * @throws IllegalStateException if {@code expression} is false
    */
   public static void checkState(boolean expression) {
     if (!expression) {
       throw new IllegalStateException();
     }
   }

   /**
    * Ensures the truth of an expression involving the state of the calling
    * instance, but not involving any parameters to the calling method.
    *
    * @param expression a boolean expression
    * @param errorMessage the exception message to use if the check fails; will
    *     be converted to a string using {@link String#valueOf(Object)}
    * @throws IllegalStateException if {@code expression} is false
    */
   public static void checkState(boolean expression, Object errorMessage) {
     if (!expression) {
       throw new IllegalStateException(String.valueOf(errorMessage));
     }
   }

   /**
    * Ensures the truth of an expression involving the state of the calling
    * instance, but not involving any parameters to the calling method.
    *
    * @param expression a boolean expression
    * @param errorMessageTemplate a template for the exception message should the
    *     check fail. The message is formed by replacing each {@code %s}
    *     placeholder in the template with an argument. These are matched by
    *     position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
    *     Unmatched arguments will be appended to the formatted message in square
    *     braces. Unmatched placeholders will be left as-is.
    * @param errorMessageArgs the arguments to be substituted into the message
    *     template. Arguments are converted to strings using
    *     {@link String#valueOf(Object)}.
    * @throws IllegalStateException if {@code expression} is false
    * @throws NullPointerException if the check fails and either {@code
    *     errorMessageTemplate} or {@code errorMessageArgs} is null (don't let
    *     this happen)
    */
   public static void checkState(boolean expression,
       String errorMessageTemplate, Object... errorMessageArgs) {
     if (!expression) {
       throw new IllegalStateException(
           format(errorMessageTemplate, errorMessageArgs));
     }
   }

   /**
    * Substitutes each {@code %s} in {@code template} with an argument. These
    * are matched by position - the first {@code %s} gets {@code args[0]}, etc.
    * If there are more arguments than placeholders, the unmatched arguments will
    * be appended to the end of the formatted message in square braces.
    *
    * @param template a non-null string containing 0 or more {@code %s}
    *     placeholders.
    * @param args the arguments to be substituted into the message
    *     template. Arguments are converted to strings using
    *     {@link String#valueOf(Object)}. Arguments can be null.
    */
   static String format(String template, Object... args) {
     // start substituting the arguments into the '%s' placeholders
     StringBuilder builder = new StringBuilder(
         template.length() + 16 * args.length);
     int templateStart = 0;
     int i = 0;
     while (i < args.length) {
       int placeholderStart = template.indexOf("%s", templateStart);
       if (placeholderStart == -1) {
         break;
       }
       builder.append(template.substring(templateStart, placeholderStart));
       builder.append(args[i++]);
       templateStart = placeholderStart + 2;
     }
     builder.append(template.substring(templateStart));

     // if we run out of placeholders, append the extra args in square braces
     if (i < args.length) {
       builder.append(" [");
       builder.append(args[i++]);
       while (i < args.length) {
         builder.append(", ");
         builder.append(args[i++]);
       }
       builder.append("]");
     }

     return builder.toString();
   }

   private static String badElementIndex(int index, int size, String desc) {
     if (index < 0) {
       return format("%s (%s) must not be negative", desc, index);
     } else if (size < 0) {
       throw new IllegalArgumentException("negative size: " + size);
     } else { // index >= size
       return format("%s (%s) must be less than size (%s)", desc, index, size);
     }
   }

   private static String badPositionIndex(int index, int size, String desc) {
     if (index < 0) {
       return format("%s (%s) must not be negative", desc, index);
     } else if (size < 0) {
       throw new IllegalArgumentException("negative size: " + size);
     } else { // index > size
       return format("%s (%s) must not be greater than size (%s)",
                     desc, index, size);
     }
   }

   private static String badPositionIndexes(int start, int end, int size) {
     if (start < 0 || start > size) {
       return badPositionIndex(start, size, "start index");
     }
     if (end < 0 || end > size) {
       return badPositionIndex(end, size, "end index");
     }
     // end < start
     return format("end index (%s) must not be less than start index (%s)",
                   end, start);
   }

   private Preconditions() {
     // static methods class only
   }
 }
	/*
	* Copyright 2009 Google Inc.
	*
	* Licensed under the Apache License, Version 2.0 (the "License"); you may not
	* use this file except in compliance with the License. You may obtain a copy of
	* the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
	* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
	* License for the specific language governing permissions and limitations under
	* the License.
	*/
	package com.google.gwt.dev.util;

	/**
	* Simple static methods to be called at the start of your own methods to verify
	* correct arguments and state. This allows constructs such as
	* <pre>
	* if (count <= 0) {
	* throw new IllegalArgumentException("must be positive: " + count);
	* }</pre>
	*
	* to be replaced with the more compact
	* <pre>
	* checkArgument(count > 0, "must be positive: %s", count);</pre>
	*
	* Note that the sense of the expression is inverted; with {@code Preconditions}
	* you declare what you expect to be <i>true</i>, just as you do with an
	* <a href="http://java.sun.com/j2se/1.5.0/docs/guide/language/assert.html">
	* {@code assert}</a> or a JUnit {@code assertTrue} call.
	*
	* <p><b>Warning:</b> only the {@code "%s"} specifier is recognized as a
	* placeholder in these messages, not the full range of {@link
	* String#format(String, Object[])} specifiers.
	*
	* <p>Take care not to confuse precondition checking with other similar types
	* of checks! Precondition exceptions -- including those provided here, but also
	* {@link IndexOutOfBoundsException}, {@link
	* UnsupportedOperationException} and others -- are used to signal that the
	* <i>calling method</i> has made an error. This tells the caller that it should
	* not have invoked the method when it did, with the arguments it did, or
	* perhaps ever. Postcondition or other invariant failures should not throw
	* these types of exceptions.
	*
	* <p>This class was adapted from google-collections project.
	*/
	public final class Preconditions {
	/**
	* Ensures the truth of an expression involving one or more parameters to the
	* calling method.
	*
	* @param expression a boolean expression
	* @throws IllegalArgumentException if {@code expression} is false
	*/
	public static void checkArgument(boolean expression) {
	if (!expression) {
	throw new IllegalArgumentException();
	}
	}

	/**
	* Ensures the truth of an expression involving one or more parameters to the
	* calling method.
	*
	* @param expression a boolean expression
	* @param errorMessage the exception message to use if the check fails; will
	* be converted to a string using {@link String#valueOf(Object)}
	* @throws IllegalArgumentException if {@code expression} is false
	*/
	public static void checkArgument(boolean expression, Object errorMessage) {
	if (!expression) {
	throw new IllegalArgumentException(String.valueOf(errorMessage));
	}
	}

	/**
	* Ensures the truth of an expression involving one or more parameters to the
	* calling method.
	*
	* @param expression a boolean expression
	* @param errorMessageTemplate a template for the exception message should the
	* check fail. The message is formed by replacing each {@code %s}
	* placeholder in the template with an argument. These are matched by
	* position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
	* Unmatched arguments will be appended to the formatted message in square
	* braces. Unmatched placeholders will be left as-is.
	* @param errorMessageArgs the arguments to be substituted into the message
	* template. Arguments are converted to strings using
	* {@link String#valueOf(Object)}.
	* @throws IllegalArgumentException if {@code expression} is false
	* @throws NullPointerException if the check fails and either {@code
	* errorMessageTemplate} or {@code errorMessageArgs} is null (don't let
	* this happen)
	*/
	public static void checkArgument(boolean expression,
	String errorMessageTemplate, Object... errorMessageArgs) {
	if (!expression) {
	throw new IllegalArgumentException(
	format(errorMessageTemplate, errorMessageArgs));
	}
	}

	/**
	* Ensures that {@code index} specifies a valid <i>element</i> in an array,
	* list or string of size {@code size}. An element index may range from zero,
	* inclusive, to {@code size}, exclusive.
	*
	* @param index a user-supplied index identifying an element of an array, list
	* or string
	* @param size the size of that array, list or string
	* @return the value of {@code index}
	* @throws IndexOutOfBoundsException if {@code index} is negative or is not
	* less than {@code size}
	* @throws IllegalArgumentException if {@code size} is negative
	*/
	public static int checkElementIndex(int index, int size) {
	return checkElementIndex(index, size, "index");
	}

	/**
	* Ensures that {@code index} specifies a valid <i>element</i> in an array,
	* list or string of size {@code size}. An element index may range from zero,
	* inclusive, to {@code size}, exclusive.
	*
	* @param index a user-supplied index identifying an element of an array, list
	* or string
	* @param size the size of that array, list or string
	* @param desc the text to use to describe this index in an error message
	* @return the value of {@code index}
	* @throws IndexOutOfBoundsException if {@code index} is negative or is not
	* less than {@code size}
	* @throws IllegalArgumentException if {@code size} is negative
	*/
	public static int checkElementIndex(int index, int size, String desc) {
	// Carefully optimized for execution by hotspot (explanatory comment above)
	if (index < 0 \|\| index >= size) {
	throw new IndexOutOfBoundsException(badElementIndex(index, size, desc));
	}
	return index;
	}

	/**
	* Ensures that an object reference passed as a parameter to the calling
	* method is not null.
	*
	* @param reference an object reference
	* @return the non-null reference that was validated
	* @throws NullPointerException if {@code reference} is null
	*/
	public static <T> T checkNotNull(T reference) {
	if (reference == null) {
	throw new NullPointerException();
	}
	return reference;
	}

	/**
	* Ensures that an object reference passed as a parameter to the calling
	* method is not null.
	*
	* @param reference an object reference
	* @param errorMessage the exception message to use if the check fails; will
	* be converted to a string using {@link String#valueOf(Object)}
	* @return the non-null reference that was validated
	* @throws NullPointerException if {@code reference} is null
	*/
	public static <T> T checkNotNull(T reference, Object errorMessage) {
	if (reference == null) {
	throw new NullPointerException(String.valueOf(errorMessage));
	}
	return reference;
	}

	/**
	* Ensures that an object reference passed as a parameter to the calling
	* method is not null.
	*
	* @param reference an object reference
	* @param errorMessageTemplate a template for the exception message should the
	* check fail. The message is formed by replacing each {@code %s}
	* placeholder in the template with an argument. These are matched by
	* position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
	* Unmatched arguments will be appended to the formatted message in square
	* braces. Unmatched placeholders will be left as-is.
	* @param errorMessageArgs the arguments to be substituted into the message
	* template. Arguments are converted to strings using
	* {@link String#valueOf(Object)}.
	* @return the non-null reference that was validated
	* @throws NullPointerException if {@code reference} is null
	*/
	public static <T> T checkNotNull(T reference, String errorMessageTemplate,
	Object... errorMessageArgs) {
	if (reference == null) {
	// If either of these parameters is null, the right thing happens anyway
	throw new NullPointerException(
	format(errorMessageTemplate, errorMessageArgs));
	}
	return reference;
	}

	/**
	* Ensures that {@code index} specifies a valid <i>position</i> in an array,
	* list or string of size {@code size}. A position index may range from zero
	* to {@code size}, inclusive.
	*
	* @param index a user-supplied index identifying a position in an array, list
	* or string
	* @param size the size of that array, list or string
	* @return the value of {@code index}
	* @throws IndexOutOfBoundsException if {@code index} is negative or is
	* greater than {@code size}
	* @throws IllegalArgumentException if {@code size} is negative
	*/
	public static int checkPositionIndex(int index, int size) {
	return checkPositionIndex(index, size, "index");
	}

	/**
	* Ensures that {@code index} specifies a valid <i>position</i> in an array,
	* list or string of size {@code size}. A position index may range from zero
	* to {@code size}, inclusive.
	*
	* @param index a user-supplied index identifying a position in an array, list
	* or string
	* @param size the size of that array, list or string
	* @param desc the text to use to describe this index in an error message
	* @return the value of {@code index}
	* @throws IndexOutOfBoundsException if {@code index} is negative or is
	* greater than {@code size}
	* @throws IllegalArgumentException if {@code size} is negative
	*/
	public static int checkPositionIndex(int index, int size, String desc) {
	// Carefully optimized for execution by hotspot (explanatory comment above)
	if (index < 0 \|\| index > size) {
	throw new IndexOutOfBoundsException(badPositionIndex(index, size, desc));
	}
	return index;
	}

	/**
	* Ensures that {@code start} and {@code end} specify a valid <i>positions</i>
	* in an array, list or string of size {@code size}, and are in order. A
	* position index may range from zero to {@code size}, inclusive.
	*
	* @param start a user-supplied index identifying a starting position in an
	* array, list or string
	* @param end a user-supplied index identifying a ending position in an array,
	* list or string
	* @param size the size of that array, list or string
	* @throws IndexOutOfBoundsException if either index is negative or is
	* greater than {@code size}, or if {@code end} is less than {@code start}
	* @throws IllegalArgumentException if {@code size} is negative
	*/
	public static void checkPositionIndexes(int start, int end, int size) {
	// Carefully optimized for execution by hotspot (explanatory comment above)
	if (start < 0 \|\| end < start \|\| end > size) {
	throw new IndexOutOfBoundsException(badPositionIndexes(start, end, size));
	}
	}

	/**
	* Ensures the truth of an expression involving the state of the calling
	* instance, but not involving any parameters to the calling method.
	*
	* @param expression a boolean expression
	* @throws IllegalStateException if {@code expression} is false
	*/
	public static void checkState(boolean expression) {
	if (!expression) {
	throw new IllegalStateException();
	}
	}

	/**
	* Ensures the truth of an expression involving the state of the calling
	* instance, but not involving any parameters to the calling method.
	*
	* @param expression a boolean expression
	* @param errorMessage the exception message to use if the check fails; will
	* be converted to a string using {@link String#valueOf(Object)}
	* @throws IllegalStateException if {@code expression} is false
	*/
	public static void checkState(boolean expression, Object errorMessage) {
	if (!expression) {
	throw new IllegalStateException(String.valueOf(errorMessage));
	}
	}

	/**
	* Ensures the truth of an expression involving the state of the calling
	* instance, but not involving any parameters to the calling method.
	*
	* @param expression a boolean expression
	* @param errorMessageTemplate a template for the exception message should the
	* check fail. The message is formed by replacing each {@code %s}
	* placeholder in the template with an argument. These are matched by
	* position - the first {@code %s} gets {@code errorMessageArgs[0]}, etc.
	* Unmatched arguments will be appended to the formatted message in square
	* braces. Unmatched placeholders will be left as-is.
	* @param errorMessageArgs the arguments to be substituted into the message
	* template. Arguments are converted to strings using
	* {@link String#valueOf(Object)}.
	* @throws IllegalStateException if {@code expression} is false
	* @throws NullPointerException if the check fails and either {@code
	* errorMessageTemplate} or {@code errorMessageArgs} is null (don't let
	* this happen)
	*/
	public static void checkState(boolean expression,
	String errorMessageTemplate, Object... errorMessageArgs) {
	if (!expression) {
	throw new IllegalStateException(
	format(errorMessageTemplate, errorMessageArgs));
	}
	}

	/**
	* Substitutes each {@code %s} in {@code template} with an argument. These
	* are matched by position - the first {@code %s} gets {@code args[0]}, etc.
	* If there are more arguments than placeholders, the unmatched arguments will
	* be appended to the end of the formatted message in square braces.
	*
	* @param template a non-null string containing 0 or more {@code %s}
	* placeholders.
	* @param args the arguments to be substituted into the message
	* template. Arguments are converted to strings using
	* {@link String#valueOf(Object)}. Arguments can be null.
	*/
	static String format(String template, Object... args) {
	// start substituting the arguments into the '%s' placeholders
	StringBuilder builder = new StringBuilder(
	template.length() + 16 * args.length);
	int templateStart = 0;
	int i = 0;
	while (i < args.length) {
	int placeholderStart = template.indexOf("%s", templateStart);
	if (placeholderStart == -1) {
	break;
	}
	builder.append(template.substring(templateStart, placeholderStart));
	builder.append(args[i++]);
	templateStart = placeholderStart + 2;
	}
	builder.append(template.substring(templateStart));

	// if we run out of placeholders, append the extra args in square braces
	if (i < args.length) {
	builder.append(" [");
	builder.append(args[i++]);
	while (i < args.length) {
	builder.append(", ");
	builder.append(args[i++]);
	}
	builder.append("]");
	}

	return builder.toString();
	}

	private static String badElementIndex(int index, int size, String desc) {
	if (index < 0) {
	return format("%s (%s) must not be negative", desc, index);
	} else if (size < 0) {
	throw new IllegalArgumentException("negative size: " + size);
	} else { // index >= size
	return format("%s (%s) must be less than size (%s)", desc, index, size);
	}
	}

	private static String badPositionIndex(int index, int size, String desc) {
	if (index < 0) {
	return format("%s (%s) must not be negative", desc, index);
	} else if (size < 0) {
	throw new IllegalArgumentException("negative size: " + size);
	} else { // index > size
	return format("%s (%s) must not be greater than size (%s)",
	desc, index, size);
	}
	}

	private static String badPositionIndexes(int start, int end, int size) {
	if (start < 0 \|\| start > size) {
	return badPositionIndex(start, size, "start index");
	}
	if (end < 0 \|\| end > size) {
	return badPositionIndex(end, size, "end index");
	}
	// end < start
	return format("end index (%s) must not be less than start index (%s)",
	end, start);
	}

	private Preconditions() {
	// static methods class only
	}
	}