Class: java.lang.management.MemoryUsage

  • public class MemoryUsage
A MemoryUsage object represents a snapshot of memory usage. Instances of the MemoryUsage class are usually constructed by methods that are used to obtain memory usage information about individual memory pool of the Java virtual machine or the heap or non-heap memory of the Java virtual machine as a whole.

A MemoryUsage object contains four values:

    init represents the initial amount of memory (in bytes) that the Java virtual machine requests from the operating system for memory management during startup. The Java virtual machine may request additional memory from the operating system and may also release memory to the system over time. The value of init may be undefined.
    used represents the amount of memory currently used (in bytes).
    committed represents the amount of memory (in bytes) that is guaranteed to be available for use by the Java virtual machine. The amount of committed memory may change over time (increase or decrease). The Java virtual machine may release memory to the system and committed could be less than init. committed will always be greater than or equal to used.
    max represents the maximum amount of memory (in bytes) that can be used for memory management. Its value may be undefined. The maximum amount of memory may change over time if defined. The amount of used and committed memory will always be less than or equal to max if max is defined. A memory allocation may fail if it attempts to increase the used memory such that used > committed even if used <= max would still be true (for example, when the system is low on virtual memory).
    Below is a picture showing an example of a memory pool: 

            +----------------------------------------------+
        +////////////////           |                  +
        +////////////////           |                  +
        +----------------------------------------------+

        |--------|
           init
        |---------------|
               used
        |---------------------------|
                  committed
        |----------------------------------------------|
                            max

    MXBean Mapping

    MemoryUsage is mapped to a CompositeData with attributes as specified in the from method.
    Authors:
    @author Mandy Chung
    Since:
    @since 1.5

    Inheritance

    Superclass tree:

    Methods

    • MemoryUsagetop

      public MemoryUsage(long init, long used, long committed, long max)
      Constructs a MemoryUsage object.
      Parameters:
      @param init the initial amount of memory in bytes that the Java virtual machine allocates; or -1 if undefined.
      @param used the amount of used memory in bytes.
      @param committed the amount of committed memory in bytes.
      @param max the maximum amount of memory in bytes that can be used; or -1 if undefined.
      Exceptions:
      @throws IllegalArgumentException if
      • the value of init or max is negative but not -1; or
      • the value of used or committed is negative; or
      • used is greater than the value of committed; or
      • committed is greater than the value of max max if defined.
      Related Links:
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    • MemoryUsagetop

      private MemoryUsage(CompositeData cd)
      Constructs a MemoryUsage object from a CompositeData.
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    • fromtop

      public static MemoryUsage from(CompositeData cd)
      Returns a MemoryUsage object represented by the given CompositeData. The given CompositeData must contain the following attributes:

      Attribute NameType
      initjava.lang.Long
      usedjava.lang.Long
      committedjava.lang.Long
      maxjava.lang.Long
      Parameters:
      @param cd CompositeData representing a MemoryUsage
      Return:
      @return a MemoryUsage object represented by cd if cd is not null; null otherwise.
      Exceptions:
      @throws IllegalArgumentException if cd does not represent a MemoryUsage with the attributes described above.
      Related Links:
      Google Code Search
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    • getCommittedtop

      public long getCommitted()
      Returns the amount of memory in bytes that is committed for the Java virtual machine to use. This amount of memory is guaranteed for the Java virtual machine to use.
      Return:
      @return the amount of committed memory in bytes.
      Related Links:
      Google Code Search
      Stack Overflow

    • getInittop

      public long getInit()
      Returns the amount of memory in bytes that the Java virtual machine initially requests from the operating system for memory management. This method returns -1 if the initial memory size is undefined.
      Return:
      @return the initial size of memory in bytes; -1 if undefined.
      Related Links:
      Google Code Search
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    • getMaxtop

      public long getMax()
      Returns the maximum amount of memory in bytes that can be used for memory management. This method returns -1 if the maximum memory size is undefined.

      This amount of memory is not guaranteed to be available for memory management if it is greater than the amount of committed memory. The Java virtual machine may fail to allocate memory even if the amount of used memory does not exceed this maximum size.

      Return:
      @return the maximum amount of memory in bytes; -1 if undefined.
      Related Links:
      Google Code Search
      Stack Overflow

    • getUsedtop

      public long getUsed()
      Returns the amount of used memory in bytes.
      Return:
      @return the amount of used memory in bytes.
      Related Links:
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    • toStringtop

      public String toString()
      Returns a descriptive representation of this memory usage.
      Return:
      @return a string representation of the object.
      Override hierarchy:
      toString from Object
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    Fields

    • committed

      final private long committed

    • init

      final private long init

    • max

      final private long max

    • used

      final private long used