Java Certificat Prep: OCA (1Z0-808) & OCP (1Z0-829, 1Z0-830)

Explore the environment for Java development by identifying the JDK and JRE components, mastering commands javac, java, jar, and javadoc, and understanding cross-platform class bytecode.

Explore the Java main method and its public static void and String[] args signature, showing how programs start and how command-line arguments are processed.

Explore how Java packages organize classes as folders, how imports, fully qualified names, and wildcards enable usage, and how to create and structure custom packages for reliable code.

Explore Java data types, including boolean, byte, short, int, long, float, double, and char, along with wrapper classes and strings, covering default values, ranges, suffix rules, bases, and parsing.

Local variable type inference uses the var keyword to let the compiler infer a type from the assigned value, applies only to local variables, and the inferred type cannot change.

Master the assignment operator in Java, its lowest precedence, auto and explicit casting, compound forms, and the fact that assignment returns a value—watch exam tricks with if statements.

Learn how Java comparison operators return booleans, including equals and reference equality, relational operators, instanceof, and short-circuit behavior of logical and ternary operators.

Master flow control with if-else statements, boolean expressions, and optional else if and else blocks. See an example using a, b, c and a string s to show evaluation order.

Explore the switch statement in Java 8 syntax and its readability benefits over if-else. Learn break and default behavior, allowed types, and how grouping values works, with practical grid examples.

Master the do-while loop in Java, learning that its body runs at least once, differs from a while loop, and supports break, continue, and nested patterns.

Master strings and string methods in Java, including creation, concatenation rules, length, indexOf, substring, case conversion, equals, equalsIgnoreCase, trimming, replacing, and formatting.

Explore stringbuilder in Java, a mutable string helper with append, insert, delete, reverse. Learn how it differs from strings, and that substring does not mutate the builder.

Explore how the Java string pool stores literals in memory, how references reuse a single object, and how compile-time concatenation, runtime methods, intern, and new affect memory usage.

Explore how to declare and initialize arrays in Java, including various syntax forms, printing arrays, and understanding that arrays don't implement the equals method and have a length property.

Examine two dimensional arrays as arrays of arrays in Java, with zero-based indices and varying subarray lengths. Use nested for loops or for-each loops to access and print elements.

Compare local and instance variables, covering scope, initialization, and default values. Explain final and effectively final, and outline access modifiers, plus how final references differ from mutable content.

Explore variable arguments (varargs) and learn that a method can have one varargs parameter, which must be last, enabling a method to accept multiple strings or a string array.

Learn how static members belong to the class rather than any instance, how static fields share state, how static methods are invoked, and how static blocks and imports initialize constants.

Explore boxing and unboxing in Java, converting primitives to wrapper classes and back, including explicit boxing, auto boxing, and unboxing, with implications for overload resolution.

Define constructors as special methods called during object creation, matching the class name and lacking a return type. Explore overloading, default constructors, and private constructors with practical examples.

Learn how to use this and super in Java constructors to call other constructors or superclass constructors, and master the rules to avoid cycles and compile errors.

Explore the order of initialization in Java, showing how superclass initialization, static fields, and static initializers run once, followed by instance variables, initializers, and constructors.