Cheat sheets / Java for SDETs
Java for SDETs
The Java you are asked to write and explain in automation interviews.
OOP in a framework
- Encapsulation
- Page objects hide locators behind methods.
- Inheritance vs composition
- Keep base classes thin; pass helpers in rather than extending deep chains.
- Abstract class vs interface
- Shared state and partial code vs a pure contract; a class can implement many interfaces.
Collections
- List / Set / Map
- Ordered with duplicates; unique; key-value.
- HashMap vs TreeMap vs LinkedHashMap
- Fast and unordered; sorted by key; insertion order.
- equals and hashCode
- Override both together or HashMap and HashSet misbehave.
Common coding tasks
- Reverse a string
- StringBuilder.reverse(), or a loop from the end.
- Count characters
- Map<Character,Integer> with merge.
- Find duplicates
- Add to a Set; if add returns false it is a duplicate.
new StringBuilder(s).reverse().toString()map.merge(c, 1, Integer::sum);Exceptions and strings
- Checked vs unchecked
- Checked must be handled or declared; unchecked are runtime errors.
- String vs StringBuilder
- Strings are immutable; use StringBuilder for repeated edits.
- == vs equals
- Reference comparison vs value comparison.