Java code visualizer
Free online Java visualizer: run Java step by step and see every variable, method call and frame, with objects and arrays on the heap and each line explained.
About the Java code visualizer
StepVioz checks your program the way javac does, so a mistake is reported before anything runs, in javac's own words. Then it runs the program in your browser and records every step: each method's frame with its variables, and arrays, objects, ArrayLists and HashMaps drawn on the heap with arrows from the variables that refer to them.
Two names for one object show as two arrows to one box, which is what makes references click. Calls, return values, static fields, loop conditions worked out with their values, and exceptions as they travel up the stack are all shown. Scanner reads from the input box.