GcInfo (Java SE 9 & JDK 9 )
Keywords: com.sun.management.GcInfo class

Module jdk.management
Package com.sun.management

## Class GcInfo

- java.lang.Object
- - com.sun.management.GcInfo

- All Implemented Interfaces:
    `CompositeData`, `CompositeDataView`

      public class GcInfo
      extends Object
      implements CompositeData, CompositeDataView

  Garbage collection information. It contains the following information for one garbage collection as well as GC-specific attributes:

  > - Start time
  > - End time
  > - Duration
  > - Memory usage before the collection starts
  > - Memory usage after the collection ends

  `GcInfo` is a `CompositeData` The GC-specific attributes can be obtained via the CompositeData interface. This is a historical relic, and other classes should not copy this pattern. Use `CompositeDataView` instead.

  ### MXBean Mapping

  `GcInfo` is mapped to a `CompositeData` with attributes as specified in the `from` method.
  Since:
    1.5

- - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `boolean` | `containsKey​(String key)` | Returns `true` if and only if this `CompositeData` instance contains an item whose name is `key`.
    `boolean` | `containsValue​(Object value)` | Returns `true` if and only if this `CompositeData` instance contains an item whose value is `value`.
    `boolean` | `equals​(Object obj)` | Indicates whether some other object is "equal to" this one.
    `static GcInfo` | `from​(CompositeData cd)` | Returns a `GcInfo` object represented by the given `CompositeData`.
    `Object` | `get​(String key)` | Returns the value of the item whose name is `key`.
    `Object[]` | `getAll​(String[] keys)` | Returns an array of the values of the items whose names are specified by `keys`, in the same order as `keys`.
    `CompositeType` | `getCompositeType​()` | Returns the composite type of this composite data instance.
    `long` | `getDuration​()` | Returns the elapsed time of this GC in milliseconds.
    `long` | `getEndTime​()` | Returns the end time of this GC in milliseconds since the Java virtual machine was started.
    `long` | `getId​()` | Returns the identifier of this garbage collection which is the number of collections that this collector has done.
    `Map<String,MemoryUsage>` | `getMemoryUsageAfterGc​()` | Returns the memory usage of all memory pools at the end of this GC.
    `Map<String,MemoryUsage>` | `getMemoryUsageBeforeGc​()` | Returns the memory usage of all memory pools at the beginning of this GC.
    `long` | `getStartTime​()` | Returns the start time of this GC in milliseconds since the Java virtual machine was started.
    `int` | `hashCode​()` | Returns a hash code value for the object.
    `CompositeData` | `toCompositeData​(CompositeType ct)` | Return the `CompositeData` representation of this `GcInfo`, including any GC-specific attributes.
    `String` | `toString​()` | Returns a string representation of the object.
    `Collection<?>` | `values​()` | Returns an unmodifiable Collection view of the item values contained in this `CompositeData` instance.

    - ### Methods inherited from class java.lang.Object

      `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

- - ### Method Detail

    - #### getId

          public long getId​()

      Returns the identifier of this garbage collection which is the number of collections that this collector has done.
      Returns:
        the identifier of this garbage collection which is the number of collections that this collector has done.

    - #### getStartTime

          public long getStartTime​()

      Returns the start time of this GC in milliseconds since the Java virtual machine was started.
      Returns:
        the start time of this GC.

    - #### getEndTime

          public long getEndTime​()

      Returns the end time of this GC in milliseconds since the Java virtual machine was started.
      Returns:
        the end time of this GC.

    - #### getDuration

          public long getDuration​()

      Returns the elapsed time of this GC in milliseconds.
      Returns:
        the elapsed time of this GC in milliseconds.

    - #### getMemoryUsageBeforeGc

          public Map<String,MemoryUsage> getMemoryUsageBeforeGc​()

      Returns the memory usage of all memory pools at the beginning of this GC. This method returns a `Map` of the name of a memory pool to the memory usage of the corresponding memory pool before GC starts.
      Returns:
        a `Map` of memory pool names to the memory usage of a memory pool before GC starts.

    - #### getMemoryUsageAfterGc

          public Map<String,MemoryUsage> getMemoryUsageAfterGc​()

      Returns the memory usage of all memory pools at the end of this GC. This method returns a `Map` of the name of a memory pool to the memory usage of the corresponding memory pool when GC finishes.
      Returns:
        a `Map` of memory pool names to the memory usage of a memory pool when GC finishes.

    - #### from

          public static GcInfo from​(CompositeData cd)

      Returns a `GcInfo` object represented by the given `CompositeData`. The given `CompositeData` must contain all the following attributes:

      > description
      > Attribute Name | Type
      > --- | ---
      > index | `java.lang.Long`
      > startTime | `java.lang.Long`
      > endTime | `java.lang.Long`
      > memoryUsageBeforeGc | `javax.management.openmbean.TabularData`
      > memoryUsageAfterGc | `javax.management.openmbean.TabularData`

      Returns:
        a `GcInfo` object represented by `cd` if `cd` is not `null`; `null` otherwise.
      Throws:
        `IllegalArgumentException` - if `cd` does not represent a `GcInfo` object with the attributes described above.

    - #### containsKey

          public boolean containsKey​(String key)

      Description copied from interface: `CompositeData`
      Returns `true` if and only if this `CompositeData` instance contains an item whose name is `key`. If `key` is a null or empty String, this method simply returns false.
      Specified by:
        `containsKey` in interface `CompositeData`
      Parameters:
        `key` - the key to be tested.
      Returns:
        true if this `CompositeData` contains the key.

    - #### containsValue

          public boolean containsValue​(Object value)

      Description copied from interface: `CompositeData`
      Returns `true` if and only if this `CompositeData` instance contains an item whose value is `value`.
      Specified by:
        `containsValue` in interface `CompositeData`
      Parameters:
        `value` - the value to be tested.
      Returns:
        true if this `CompositeData` contains the value.

    - #### equals

          public boolean equals​(Object obj)

      Description copied from class: `Object`
      Indicates whether some other object is "equal to" this one.

      The `equals` method implements an equivalence relation on non-null object references:

      - It is reflexive: for any non-null reference value `x`, `x.equals(x)` should return `true`.
      - It is symmetric: for any non-null reference values `x` and `y`, `x.equals(y)` should return `true` if and only if `y.equals(x)` returns `true`.
      - It is transitive: for any non-null reference values `x`, `y`, and `z`, if `x.equals(y)` returns `true` and `y.equals(z)` returns `true`, then `x.equals(z)` should return `true`.
      - It is consistent: for any non-null reference values `x` and `y`, multiple invocations of `x.equals(y)` consistently return `true` or consistently return `false`, provided no information used in `equals` comparisons on the objects is modified.
      - For any non-null reference value `x`, `x.equals(null)` should return `false`.

      The `equals` method for class `Object` implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values `x` and `y`, this method returns `true` if and only if `x` and `y` refer to the same object (`x == y` has the value `true`).

      Note that it is generally necessary to override the `hashCode` method whenever this method is overridden, so as to maintain the general contract for the `hashCode` method, which states that equal objects must have equal hash codes.

      Specified by:
        `equals` in interface `CompositeData`
      Overrides:
        `equals` in class `Object`
      Parameters:
        `obj` - the reference object with which to compare.
      Returns:
        `true` if this object is the same as the obj argument; `false` otherwise.
      See Also:
        `Object.hashCode()`, `HashMap`

    - #### get

          public Object get​(String key)

      Description copied from interface: `CompositeData`
      Returns the value of the item whose name is `key`.
      Specified by:
        `get` in interface `CompositeData`
      Parameters:
        `key` - the name of the item.
      Returns:
        the value associated with this key.

    - #### getAll

          public Object[] getAll​(String[] keys)

      Description copied from interface: `CompositeData`
      Returns an array of the values of the items whose names are specified by `keys`, in the same order as `keys`.
      Specified by:
        `getAll` in interface `CompositeData`
      Parameters:
        `keys` - the names of the items.
      Returns:
        the values corresponding to the keys.

    - #### getCompositeType

          public CompositeType getCompositeType​()

      Description copied from interface: `CompositeData`
      Returns the composite type of this composite data instance.
      Specified by:
        `getCompositeType` in interface `CompositeData`
      Returns:
        the type of this CompositeData.

    - #### hashCode

          public int hashCode​()

      Description copied from class: `Object`
      Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by `HashMap`.

      The general contract of `hashCode` is:

      - Whenever it is invoked on the same object more than once during an execution of a Java application, the `hashCode` method must consistently return the same integer, provided no information used in `equals` comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
      - If two objects are equal according to the `equals(Object)` method, then calling the `hashCode` method on each of the two objects must produce the same integer result.
      - It is not required that if two objects are unequal according to the `Object.equals(java.lang.Object)` method, then calling the `hashCode` method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.

      As much as is reasonably practical, the hashCode method defined by class `Object` does return distinct integers for distinct objects. (The hashCode may or may not be implemented as some function of an object's memory address at some point in time.)

      Specified by:
        `hashCode` in interface `CompositeData`
      Overrides:
        `hashCode` in class `Object`
      Returns:
        a hash code value for this object.
      See Also:
        `Object.equals(java.lang.Object)`, `System.identityHashCode(java.lang.Object)`

    - #### toString

          public String toString​()

      Description copied from class: `Object`
      Returns a string representation of the object. In general, the `toString` method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

      The `toString` method for class `Object` returns a string consisting of the name of the class of which the object is an instance, the at-sign character ``@`', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

      >      getClass().getName() + '@' + Integer.toHexString(hashCode())

      Specified by:
        `toString` in interface `CompositeData`
      Overrides:
        `toString` in class `Object`
      Returns:
        a string representation of the object.

    - #### values

          public Collection<?> values​()

      Description copied from interface: `CompositeData`
      Returns an unmodifiable Collection view of the item values contained in this `CompositeData` instance. The returned collection's iterator will return the values in the ascending lexicographic order of the corresponding item names.
      Specified by:
        `values` in interface `CompositeData`
      Returns:
        the values.

    - #### toCompositeData

          public CompositeData toCompositeData​(CompositeType ct)

      Return the `CompositeData` representation of this `GcInfo`, including any GC-specific attributes. The returned value will have at least all the attributes described in the `from` method, plus optionally other attributes.
      Specified by:
        `toCompositeData` in interface `CompositeDataView`
      Parameters:
        `ct` - the `CompositeType` that the caller expects. This parameter is ignored and can be null.
      Returns:
        the `CompositeData` representation.