Java flashcards, generated for you.

'==' compares object references (memory addresses); '.equals()' compares actual string content. Always use '.equals()' for string content comparison.

'null' is the absence of a value/object. Calling any method on null throws a NullPointerException (NPE) at runtime.

Primitives (int, boolean, double, etc.) store values directly on the stack; reference types (objects, arrays, strings) store a memory address on the stack pointing to data on the heap.

Java is always pass-by-value. For primitives, the value copies; for objects, the reference (address) copies. Modifying object fields inside a method affects the original; reassigning the reference parameter does not.

'final' is a modifier preventing reassignment (variables) or overriding (methods/classes); 'finally' is a block that always executes in try-catch-finally; 'finalize()' is a deprecated method called before garbage collection.

Static variables are shared across all instances of a class, stored once in memory; instance variables are created per object instance. Static variables exist even without object instantiation.

Arrays are fixed-size, type-specific, and store contiguous memory; ArrayLists are dynamic, resizable, and slower. Use arrays for fixed-size data; use ArrayList when size changes frequently.

Auto-boxing converts primitives to wrapper objects (int→Integer); auto-unboxing reverses it (Integer→int). Gotcha: unboxing a null Integer throws NullPointerException, not a default value.

Checked exceptions (IOException, SQLException) must be caught or declared in method signature; unchecked exceptions (RuntimeException, NullPointerException) are optional. Checked enforced at compile-time.

'this' refers to the current object instance; 'super' refers to the parent class. Use 'this' to access current class members or call another constructor; use 'super' to access parent class members or call parent constructor.