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Tools to obtain the amount of memory used by objects - generically known as "sizeof" tools.

(Year in brackets is when the tool/page was last updated)

• (2014) EHCache sizeof, implements an agent based sizeof; an unsafe based one; and a reflection based one; and will fallback to whatever it can achieve (see also http://codespot.net/2014/03/05/sizeof-java-library/)
• (2014) jol sizeof (uses unsafe)
• (2014) java.SizeOf utility (based on Heinz Kabutz's instrumentation agent article)
• (2013) carrotsearch RamUsageEstimator from Apache Solr/Lucene, uses unsafe
• (2012) Plumbr's implementation of instrumentation agent sizeof based on Heinz Kabutz's article
• (2009) javabi-sizeof - reflection based
• (2007) Instrumentation Memory Counter - size of based on instrumentation agent
• (2003) Javaworld article Sizeof for Java. Uses reflection and assumptions
• (2002) Javaworld Java Tip 130: Do you know your data size? (uses Runtime methods to infer sizes)