java.lang.Object
- org.apache.lucene.util.RamUsageEstimator

```
public final class RamUsageEstimator
extends Object
```
Estimates the size (memory representation) of Java objects.
NOTE: Starting with Lucene 3.6, creating instances of this class is deprecated. If you still do this, please note, that instances of RamUsageEstimator are not thread-safe! It is also deprecated to enable checking of String intern-ness, the new static method no longer allow to do this. Interned strings will be counted as any other object and count for memory usage.
In Lucene 3.6, custom MemoryModels were completely removed. The new implementation is now using Hotspot™ internals to get the correct scale factors and offsets for calculating memory usage.

See Also:

sizeOf(Object), shallowSizeOf(Object), shallowSizeOfInstance(Class)

NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

Nested Class Summary

Nested Classes
Modifier and Type Class Description

static class RamUsageEstimator.JvmFeature
JVM diagnostic features.

Field Summary

Fields
Modifier and Type	Field	Description
`static String`	`JVM_INFO_STRING`	JVM info string for debugging and reports.
`static int`	`NUM_BYTES_ARRAY_HEADER`	Number of bytes to represent an array header (no content, but with alignments).
`static int`	`NUM_BYTES_BOOLEAN`
`static int`	`NUM_BYTES_BYTE`
`static int`	`NUM_BYTES_CHAR`
`static int`	`NUM_BYTES_DOUBLE`
`static int`	`NUM_BYTES_FLOAT`
`static int`	`NUM_BYTES_INT`
`static int`	`NUM_BYTES_LONG`
`static int`	`NUM_BYTES_OBJECT_ALIGNMENT`	A constant specifying the object alignment boundary inside the JVM.
`static int`	`NUM_BYTES_OBJECT_HEADER`	Number of bytes to represent an object header (no fields, no alignments).
`static int`	`NUM_BYTES_OBJECT_REF`	Number of bytes this jvm uses to represent an object reference.
`static int`	`NUM_BYTES_SHORT`
`static long`	`ONE_GB`	One gigabyte bytes.
`static long`	`ONE_KB`	One kilobyte bytes.
`static long`	`ONE_MB`	One megabyte bytes.

Constructor Summary

Constructors
Constructor	Description
`RamUsageEstimator()`	Deprecated. Don't create instances of this class, instead use the static `sizeOf(Object)` method that has no intern checking, too.
`RamUsageEstimator(boolean checkInterned)`	Deprecated. Don't create instances of this class, instead use the static `sizeOf(Object)` method.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods Deprecated Methods
Modifier and Type	Method	Description
`static long`	`alignObjectSize(long size)`	Aligns an object size to be the next multiple of `NUM_BYTES_OBJECT_ALIGNMENT`.
`long`	`estimateRamUsage(Object obj)`	Deprecated. Don't create instances of this class, instead use the static `sizeOf(Object)` method.
`static EnumSet<RamUsageEstimator.JvmFeature>`	`getSupportedFeatures()`	Return the set of supported JVM features that improve the estimation.
`static EnumSet<RamUsageEstimator.JvmFeature>`	`getUnsupportedFeatures()`	Return the set of unsupported JVM features that improve the estimation.
`static String`	`humanReadableUnits(long bytes)`	Returns `size` in human-readable units (GB, MB, KB or bytes).
`static String`	`humanReadableUnits(long bytes, DecimalFormat df)`	Returns `size` in human-readable units (GB, MB, KB or bytes).
`static String`	`humanSizeOf(Object object)`	Return a human-readable size of a given object.
`static boolean`	`isSupportedJVM()`	Returns true, if the current JVM is fully supported by `RamUsageEstimator`.
`static long`	`shallowSizeOf(Object obj)`	Estimates a "shallow" memory usage of the given object.
`static long`	`shallowSizeOfInstance(Class<?> clazz)`	Returns the shallow instance size in bytes an instance of the given class would occupy.
`static long`	`sizeOf(boolean[] arr)`	Returns the size in bytes of the boolean[] object.
`static long`	`sizeOf(byte[] arr)`	Returns the size in bytes of the byte[] object.
`static long`	`sizeOf(char[] arr)`	Returns the size in bytes of the char[] object.
`static long`	`sizeOf(double[] arr)`	Returns the size in bytes of the double[] object.
`static long`	`sizeOf(float[] arr)`	Returns the size in bytes of the float[] object.
`static long`	`sizeOf(int[] arr)`	Returns the size in bytes of the int[] object.
`static long`	`sizeOf(long[] arr)`	Returns the size in bytes of the long[] object.
`static long`	`sizeOf(short[] arr)`	Returns the size in bytes of the short[] object.
`static long`	`sizeOf(Object obj)`	Estimates the RAM usage by the given object.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - JVM_INFO_STRING
```
public static final String JVM_INFO_STRING
```
    JVM info string for debugging and reports.
  - ONE_KB
```
public static final long ONE_KB
```
    One kilobyte bytes.
    
    See Also:
    
    Constant Field Values
  - ONE_MB
```
public static final long ONE_MB
```
    One megabyte bytes.
    
    See Also:
    
    Constant Field Values
  - ONE_GB
```
public static final long ONE_GB
```
    One gigabyte bytes.
    
    See Also:
    
    Constant Field Values
  - NUM_BYTES_BOOLEAN
```
public static final int NUM_BYTES_BOOLEAN
```
    See Also:
    
    Constant Field Values
  - NUM_BYTES_BYTE
```
public static final int NUM_BYTES_BYTE
```
    See Also:
    
    Constant Field Values
  - NUM_BYTES_CHAR
```
public static final int NUM_BYTES_CHAR
```
    See Also:
    
    Constant Field Values
  - NUM_BYTES_SHORT
```
public static final int NUM_BYTES_SHORT
```
    See Also:
    
    Constant Field Values
  - NUM_BYTES_INT
```
public static final int NUM_BYTES_INT
```
    See Also:
    
    Constant Field Values
  - NUM_BYTES_FLOAT
```
public static final int NUM_BYTES_FLOAT
```
    See Also:
    
    Constant Field Values
  - NUM_BYTES_LONG
```
public static final int NUM_BYTES_LONG
```
    See Also:
    
    Constant Field Values
  - NUM_BYTES_DOUBLE
```
public static final int NUM_BYTES_DOUBLE
```
    See Also:
    
    Constant Field Values
  - NUM_BYTES_OBJECT_REF
```
public static final int NUM_BYTES_OBJECT_REF
```
    Number of bytes this jvm uses to represent an object reference.
  - NUM_BYTES_OBJECT_HEADER
```
public static final int NUM_BYTES_OBJECT_HEADER
```
    Number of bytes to represent an object header (no fields, no alignments).
  - NUM_BYTES_ARRAY_HEADER
```
public static final int NUM_BYTES_ARRAY_HEADER
```
    Number of bytes to represent an array header (no content, but with alignments).
  - NUM_BYTES_OBJECT_ALIGNMENT
```
public static final int NUM_BYTES_OBJECT_ALIGNMENT
```
    A constant specifying the object alignment boundary inside the JVM. Objects will always take a full multiple of this constant, possibly wasting some space.
- Constructor Detail
  - RamUsageEstimator
```
@Deprecated
public RamUsageEstimator()
```
    Deprecated.
    Don't create instances of this class, instead use the static sizeOf(Object) method that has no intern checking, too.
    
    Creates a new instance of RamUsageEstimator with intern checking enabled. Don't ever use this method, as intern checking is deprecated, because it is not free of side-effects and strains the garbage collector additionally.
  - RamUsageEstimator
```
@Deprecated
public RamUsageEstimator(boolean checkInterned)
```
    Deprecated.
    Don't create instances of this class, instead use the static sizeOf(Object) method.
    
    Creates a new instance of RamUsageEstimator.
    
    Parameters:
    
    checkInterned - check if Strings are interned and don't add to size if they are. Defaults to true but if you know the objects you are checking won't likely contain many interned Strings, it will be faster to turn off intern checking. Intern checking is deprecated altogether, as it is not free of side-effects and strains the garbage collector additionally.
- Method Detail
  - isSupportedJVM
```
public static boolean isSupportedJVM()
```
    Returns true, if the current JVM is fully supported by RamUsageEstimator. If this method returns false you are maybe using a 3rd party Java VM that is not supporting Oracle/Sun private APIs. The memory estimates can be imprecise then (no way of detecting compressed references, alignments, etc.). Lucene still tries to use sensible defaults.
  - alignObjectSize
```
public static long alignObjectSize(long size)
```
    Aligns an object size to be the next multiple of NUM_BYTES_OBJECT_ALIGNMENT.
  - sizeOf
```
public static long sizeOf(byte[] arr)
```
    Returns the size in bytes of the byte[] object.
  - sizeOf
```
public static long sizeOf(boolean[] arr)
```
    Returns the size in bytes of the boolean[] object.
  - sizeOf
```
public static long sizeOf(char[] arr)
```
    Returns the size in bytes of the char[] object.
  - sizeOf
```
public static long sizeOf(short[] arr)
```
    Returns the size in bytes of the short[] object.
  - sizeOf
```
public static long sizeOf(int[] arr)
```
    Returns the size in bytes of the int[] object.
  - sizeOf
```
public static long sizeOf(float[] arr)
```
    Returns the size in bytes of the float[] object.
  - sizeOf
```
public static long sizeOf(long[] arr)
```
    Returns the size in bytes of the long[] object.
  - sizeOf
```
public static long sizeOf(double[] arr)
```
    Returns the size in bytes of the double[] object.
  - sizeOf
```
public static long sizeOf(Object obj)
```
    Estimates the RAM usage by the given object. It will walk the object tree and sum up all referenced objects.
    Resource Usage: This method internally uses a set of every object seen during traversals so it does allocate memory (it isn't side-effect free). After the method exits, this memory should be GCed.
  - shallowSizeOf
```
public static long shallowSizeOf(Object obj)
```
    Estimates a "shallow" memory usage of the given object. For arrays, this will be the memory taken by array storage (no subreferences will be followed). For objects, this will be the memory taken by the fields. JVM object alignments are also applied.
  - shallowSizeOfInstance
```
public static long shallowSizeOfInstance(Class<?> clazz)
```
    Returns the shallow instance size in bytes an instance of the given class would occupy. This works with all conventional classes and primitive types, but not with arrays (the size then depends on the number of elements and varies from object to object).
    
    Throws:
    
    IllegalArgumentException - if clazz is an array class.
    
    See Also:
    
    shallowSizeOf(Object)
  - getUnsupportedFeatures
```
public static EnumSet<RamUsageEstimator.JvmFeature> getUnsupportedFeatures()
```
    Return the set of unsupported JVM features that improve the estimation.
  - getSupportedFeatures
```
public static EnumSet<RamUsageEstimator.JvmFeature> getSupportedFeatures()
```
    Return the set of supported JVM features that improve the estimation.
  - humanReadableUnits
```
public static String humanReadableUnits(long bytes)
```
    Returns size in human-readable units (GB, MB, KB or bytes).
  - humanReadableUnits
```
public static String humanReadableUnits(long bytes,
                                        DecimalFormat df)
```
    Returns size in human-readable units (GB, MB, KB or bytes).
  - humanSizeOf
```
public static String humanSizeOf(Object object)
```
    Return a human-readable size of a given object.
    
    See Also:
    
    sizeOf(Object), humanReadableUnits(long)
  - estimateRamUsage
```
@Deprecated
public long estimateRamUsage(Object obj)
```
    Deprecated.
    Don't create instances of this class, instead use the static sizeOf(Object) method.
    
    Creates a new istance of RamUsageEstimator.
    
    See Also:
    
    sizeOf(Object)

Class RamUsageEstimator

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

JVM_INFO_STRING

ONE_KB

ONE_MB

ONE_GB

NUM_BYTES_BOOLEAN

NUM_BYTES_BYTE

NUM_BYTES_CHAR

NUM_BYTES_SHORT

NUM_BYTES_INT

NUM_BYTES_FLOAT

NUM_BYTES_LONG

NUM_BYTES_DOUBLE

NUM_BYTES_OBJECT_REF

NUM_BYTES_OBJECT_HEADER

NUM_BYTES_ARRAY_HEADER

NUM_BYTES_OBJECT_ALIGNMENT

Constructor Detail

RamUsageEstimator

RamUsageEstimator

Method Detail

isSupportedJVM

alignObjectSize

sizeOf

sizeOf

sizeOf

sizeOf

sizeOf

sizeOf

sizeOf

sizeOf

sizeOf

shallowSizeOf

shallowSizeOfInstance

getUnsupportedFeatures

getSupportedFeatures

humanReadableUnits

humanReadableUnits

humanSizeOf

estimateRamUsage