CODEWITHSUNDEEP
java
fuggy_yama
fuggy_yama

Reputation: 617

What is the memory overhead of a single entry (key-value pair) in Java 7 HashMap? (using 64-bit Oracle Hotspot JVM)

What is the memory overhead of a single entry in Java HashMap? (using 64-bit Oracle Hotspot JVM). For example: is it 24 or 32 bytes?

Upvotes: 1

Views: 162

Answers (2)

Andreas
Andreas

Reputation: 159165

The size of a HashMap.Entry (Java 6) or HashMap.Node (Java 8), both of which has one int and three references.

If a reference is 4 bytes (compressed OOPS), then 12 bytes header + 4 byte int + 3 * 4 byte reference = 28 bytes, rounded to 32 bytes to fit on 8-byte boundary.

If a reference is 8 bytes, then 16 bytes header + 4 byte int + 3 * 8 byte reference = 44 bytes, rounded to 48 bytes to fit on 8-byte boundary.

Upvotes: 1

Matteo Baldi
Matteo Baldi

Reputation: 5828

An HashMap collection takes 32 bytes for each entry plus 4 bytes * map capacity for entries array.

Upvotes: 0

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