Utils (H2 Database Engine wt-1.0.1 API)

java.lang.Object
- org.h2.util.Utils

```
public class Utils
extends Object
```
This utility class contains miscellaneous functions.

嵌套类概要

嵌套类
限定符和类型	类和说明
`static interface`	`Utils.ClassFactory` The utility methods will try to use the provided class factories to convert binary name of class to Class object.

字段概要

字段
限定符和类型字段和说明

static byte[] EMPTY_BYTES
An 0-size byte array.

static int[] EMPTY_INT_ARRAY
An 0-size int array.

字段
限定符和类型	字段和说明
`static byte[]`	`EMPTY_BYTES` An 0-size byte array.
`static int[]`	`EMPTY_INT_ARRAY` An 0-size int array.

方法概要

所有方法静态方法具体方法
限定符和类型	方法和说明
`static Object`	`callMethod(Object instance, String methodName, Object... params)` Calls an instance method via reflection.
`static Object`	`callStaticMethod(String classAndMethod, Object... params)` Calls a static method via reflection.
`static byte[]`	`cloneByteArray(byte[] b)` Create a new byte array and copy all the data.
`static int`	`compareNotNullSigned(byte[] data1, byte[] data2)` Compare the contents of two byte arrays.
`static int`	`compareNotNullUnsigned(byte[] data1, byte[] data2)` Compare the contents of two byte arrays.
`static boolean`	`compareSecure(byte[] test, byte[] good)` Compare two byte arrays.
`static byte[]`	`copy(byte[] source, byte[] target)` Copy the contents of the source array to the target array.
`static int`	`getByteArrayHash(byte[] value)` Calculate the hash code of the given byte array.
`static Object`	`getField(Object instance, String fieldName)` Returns a static field.
`static int`	`getMemoryFree()` Get the free memory in KB.
`static long`	`getMemoryMax()` Get the maximum memory in KB.
`static int`	`getMemoryUsed()` Get the used memory in KB.
`static Class<?>`	`getNonPrimitiveClass(Class<?> clazz)` Convert primitive class names to java.lang.* class names.
`static boolean`	`getProperty(String key, boolean defaultValue)` Get the system property.
`static int`	`getProperty(String key, int defaultValue)` Get the system property.
`static String`	`getProperty(String key, String defaultValue)` Get the system property.
`static byte[]`	`getResource(String name)` Get a resource from the resource map.
`static Object`	`getStaticField(String classAndField)` Returns a static field.
`static int`	`hashCode(Object o)` Calculate the hash code of the given object.
`static boolean`	`haveCommonComparableSuperclass(Class<?> c1, Class<?> c2)` Checks if given classes have a common Comparable superclass.
`static int`	`indexOf(byte[] bytes, byte[] pattern, int start)` Calculate the index of the first occurrence of the pattern in the byte array, starting with the given index.
`static boolean`	`isClassPresent(String fullyQualifiedClassName)` Returns true if the class is present in the current class loader.
`static Object`	`newInstance(String className, Object... params)` Creates a new instance.
`static int[]`	`newIntArray(int len)` Create an int array with the given size.
`static long[]`	`newLongArray(int len)` Create a long array with the given size.
`static long`	`readLong(byte[] buff, int pos)` Read a long value from the byte array at the given position.
`static int`	`scaleForAvailableMemory(int value)` Scale the value with the available memory.
`static <X> void`	`sortTopN(X[] array, int offset, int limit, Comparator<? super X> comp)` Find the top limit values using given comparator and place them as in a full array sort, in descending order.
`static void`	`writeLong(byte[] buff, int pos, long x)` Write a long value to the byte array at the given position.

从类继承的方法 java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- 字段详细资料
  - EMPTY_BYTES
```
public static final byte[] EMPTY_BYTES
```
    An 0-size byte array.
  - EMPTY_INT_ARRAY
```
public static final int[] EMPTY_INT_ARRAY
```
    An 0-size int array.
- 方法详细资料
  - writeLong
```
public static void writeLong(byte[] buff,
                             int pos,
                             long x)
```
    Write a long value to the byte array at the given position. The most significant byte is written first.
    
    参数:
    
    buff - the byte array
    
    pos - the position
    
    x - the value to write
  - readLong
```
public static long readLong(byte[] buff,
                            int pos)
```
    Read a long value from the byte array at the given position. The most significant byte is read first.
    
    参数:
    
    buff - the byte array
    
    pos - the position
    
    返回:
    
    the value
  - indexOf
```
public static int indexOf(byte[] bytes,
                          byte[] pattern,
                          int start)
```
    Calculate the index of the first occurrence of the pattern in the byte array, starting with the given index. This methods returns -1 if the pattern has not been found, and the start position if the pattern is empty.
    
    参数:
    
    bytes - the byte array
    
    pattern - the pattern
    
    start - the start index from where to search
    
    返回:
    
    the index
  - getByteArrayHash
```
public static int getByteArrayHash(byte[] value)
```
    Calculate the hash code of the given byte array.
    
    参数:
    
    value - the byte array
    
    返回:
    
    the hash code
  - compareSecure
```
public static boolean compareSecure(byte[] test,
                                    byte[] good)
```
    Compare two byte arrays. This method will always loop over all bytes and doesn't use conditional operations in the loop to make sure an attacker can not use a timing attack when trying out passwords.
    
    参数:
    
    test - the first array
    
    good - the second array
    
    返回:
    
    true if both byte arrays contain the same bytes
  - compareNotNullSigned
```
public static int compareNotNullSigned(byte[] data1,
                                       byte[] data2)
```
    Compare the contents of two byte arrays. If the content or length of the first array is smaller than the second array, -1 is returned. If the content or length of the second array is smaller than the first array, 1 is returned. If the contents and lengths are the same, 0 is returned.
    This method interprets bytes as signed.
    
    参数:
    
    data1 - the first byte array (must not be null)
    
    data2 - the second byte array (must not be null)
    
    返回:
    
    the result of the comparison (-1, 1 or 0)
  - compareNotNullUnsigned
```
public static int compareNotNullUnsigned(byte[] data1,
                                         byte[] data2)
```
    Compare the contents of two byte arrays. If the content or length of the first array is smaller than the second array, -1 is returned. If the content or length of the second array is smaller than the first array, 1 is returned. If the contents and lengths are the same, 0 is returned.
    This method interprets bytes as unsigned.
    
    参数:
    
    data1 - the first byte array (must not be null)
    
    data2 - the second byte array (must not be null)
    
    返回:
    
    the result of the comparison (-1, 1 or 0)
  - copy
```
public static byte[] copy(byte[] source,
                          byte[] target)
```
    Copy the contents of the source array to the target array. If the size if the target array is too small, a larger array is created.
    
    参数:
    
    source - the source array
    
    target - the target array
    
    返回:
    
    the target array or a new one if the target array was too small
  - cloneByteArray
```
public static byte[] cloneByteArray(byte[] b)
```
    Create a new byte array and copy all the data. If the size of the byte array is zero, the same array is returned.
    
    参数:
    
    b - the byte array (may not be null)
    
    返回:
    
    a new byte array
  - hashCode
```
public static int hashCode(Object o)
```
    Calculate the hash code of the given object. The object may be null.
    
    参数:
    
    o - the object
    
    返回:
    
    the hash code, or 0 if the object is null
  - getMemoryUsed
```
public static int getMemoryUsed()
```
    Get the used memory in KB. This method possibly calls System.gc().
    
    返回:
    
    the used memory
  - getMemoryFree
```
public static int getMemoryFree()
```
    Get the free memory in KB. This method possibly calls System.gc().
    
    返回:
    
    the free memory
  - getMemoryMax
```
public static long getMemoryMax()
```
    Get the maximum memory in KB.
    
    返回:
    
    the maximum memory
  - newIntArray
```
public static int[] newIntArray(int len)
```
    Create an int array with the given size.
    
    参数:
    
    len - the number of bytes requested
    
    返回:
    
    the int array
  - newLongArray
```
public static long[] newLongArray(int len)
```
    Create a long array with the given size.
    
    参数:
    
    len - the number of bytes requested
    
    返回:
    
    the int array
  - sortTopN
```
public static <X> void sortTopN(X[] array,
                                int offset,
                                int limit,
                                Comparator<? super X> comp)
```
    Find the top limit values using given comparator and place them as in a full array sort, in descending order.
    
    参数:
    
    array - the array.
    
    offset - the offset.
    
    limit - the limit.
    
    comp - the comparator.
  - haveCommonComparableSuperclass
```
public static boolean haveCommonComparableSuperclass(Class<?> c1,
                                                     Class<?> c2)
```
    Checks if given classes have a common Comparable superclass.
    
    参数:
    
    c1 - the first class
    
    c2 - the second class
    
    返回:
    
    true if they have
  - getResource
```
public static byte[] getResource(String name)
                          throws IOException
```
    Get a resource from the resource map.
    
    参数:
    
    name - the name of the resource
    
    返回:
    
    the resource data
    
    抛出:
    
    IOException
  - callStaticMethod
```
public static Object callStaticMethod(String classAndMethod,
                                      Object... params)
                               throws Exception
```
    Calls a static method via reflection. This will try to use the method where the most parameter classes match exactly (this algorithm is simpler than the one in the Java specification, but works well for most cases).
    
    参数:
    
    classAndMethod - a string with the entire class and method name, eg. "java.lang.System.gc"
    
    params - the method parameters
    
    返回:
    
    the return value from this call
    
    抛出:
    
    Exception
  - callMethod
```
public static Object callMethod(Object instance,
                                String methodName,
                                Object... params)
                         throws Exception
```
    Calls an instance method via reflection. This will try to use the method where the most parameter classes match exactly (this algorithm is simpler than the one in the Java specification, but works well for most cases).
    
    参数:
    
    instance - the instance on which the call is done
    
    methodName - a string with the method name
    
    params - the method parameters
    
    返回:
    
    the return value from this call
    
    抛出:
    
    Exception
  - newInstance
```
public static Object newInstance(String className,
                                 Object... params)
                          throws Exception
```
    Creates a new instance. This will try to use the constructor where the most parameter classes match exactly (this algorithm is simpler than the one in the Java specification, but works well for most cases).
    
    参数:
    
    className - a string with the entire class, eg. "java.lang.Integer"
    
    params - the constructor parameters
    
    返回:
    
    the newly created object
    
    抛出:
    
    Exception
  - getStaticField
```
public static Object getStaticField(String classAndField)
                             throws Exception
```
    Returns a static field.
    
    参数:
    
    classAndField - a string with the entire class and field name
    
    返回:
    
    the field value
    
    抛出:
    
    Exception
  - getField
```
public static Object getField(Object instance,
                              String fieldName)
                       throws Exception
```
    Returns a static field.
    
    参数:
    
    instance - the instance on which the call is done
    
    fieldName - the field name
    
    返回:
    
    the field value
    
    抛出:
    
    Exception
  - isClassPresent
```
public static boolean isClassPresent(String fullyQualifiedClassName)
```
    Returns true if the class is present in the current class loader.
    
    参数:
    
    fullyQualifiedClassName - a string with the entire class name, eg. "java.lang.System"
    
    返回:
    
    true if the class is present
  - getNonPrimitiveClass
```
public static Class<?> getNonPrimitiveClass(Class<?> clazz)
```
    Convert primitive class names to java.lang.* class names.
    
    参数:
    
    clazz - the class (for example: int)
    
    返回:
    
    the non-primitive class (for example: java.lang.Integer)
  - getProperty
```
public static String getProperty(String key,
                                 String defaultValue)
```
    Get the system property. If the system property is not set, or if a security exception occurs, the default value is returned.
    
    参数:
    
    key - the key
    
    defaultValue - the default value
    
    返回:
    
    the value
  - getProperty
```
public static int getProperty(String key,
                              int defaultValue)
```
    Get the system property. If the system property is not set, or if a security exception occurs, the default value is returned.
    
    参数:
    
    key - the key
    
    defaultValue - the default value
    
    返回:
    
    the value
  - getProperty
```
public static boolean getProperty(String key,
                                  boolean defaultValue)
```
    Get the system property. If the system property is not set, or if a security exception occurs, the default value is returned.
    
    参数:
    
    key - the key
    
    defaultValue - the default value
    
    返回:
    
    the value
  - scaleForAvailableMemory
```
public static int scaleForAvailableMemory(int value)
```
    Scale the value with the available memory. If 1 GB of RAM is available, the value is returned, if 2 GB are available, then twice the value, and so on.
    
    参数:
    
    value - the value to scale
    
    返回:
    
    the scaled value

类 Utils

嵌套类概要

字段概要

方法概要

从类继承的方法 java.lang.Object

字段详细资料

EMPTY_BYTES

EMPTY_INT_ARRAY

方法详细资料

writeLong

readLong

indexOf

getByteArrayHash

compareSecure

compareNotNullSigned

compareNotNullUnsigned

copy

cloneByteArray

hashCode

getMemoryUsed

getMemoryFree

getMemoryMax

newIntArray

newLongArray

sortTopN

haveCommonComparableSuperclass

getResource

callStaticMethod

callMethod

newInstance

getStaticField

getField

isClassPresent

getNonPrimitiveClass

getProperty

getProperty

getProperty

scaleForAvailableMemory