Java & the JVM Mind Map

Every Java & the JVM visualization on this site on one map. The branches are the main ideas. Each leaf is a page; the grey line under it is the one thing to remember about it. Click a branch to focus on it, click a page to open it.

Recall mode hides the page names. Read the hint, say the name, then click the "?" to check.

1. How the map is organized

The map at a glance: 7 branches, 28 pages.

Follow a Java program through its life, and each branch is one stage:

Before it runs: source becomes bytecode (source to bytecode), then the JVM starts and loads classes (startup).
While it runs: hot code gets compiled to machine code (JIT), and dead objects get freed (memory and GC).
What your code uses: library data structures (collections), threads and their visibility rules (threads), and frameworks that wire objects together (Spring).
Pages about Python, Go or V8 sit on the branch of the same idea, to compare with the JVM.

2. The branches side by side

Branch	When	Key idea	Typical problem
From source to bytecode	build time	portable bytecode	compile errors
Startup and class loading	start, first use of a class	parent delegation	slow start, ClassNotFoundException
JIT compilers	after code gets hot	profile, then optimise	deoptimisation, warm-up
Memory and GC	all the time	reachability from roots	pauses, OutOfMemoryError
Collections	each call	hashing, sorted tree	bad `hashCode`, resize cost
Threads and memory model	each thread	happens-before	stale values, pinning
Spring framework	context start, each call	inversion of control	self-call skips the proxy

3. Five facts to remember

javac makes portable bytecode; the JVM interprets it at first and JIT-compiles only the hot methods.
Class loaders ask their parent first, so java.lang classes always come from the bootstrap loader.
Objects live on the heap; each thread's stack holds frames with locals and references.
A tracing GC frees unreachable cycles; plain reference counting cannot.
Without volatile or synchronized, one thread may never see another thread's write.

See all Java & the JVM pages in the index, or the other mind maps.