Examples

Java examples

Understand object oriented programs and the JVM.

Java Basics

Start with a class and main method.

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Java conditions, arrays, and loops

Count values that satisfy a boundary condition.

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Java methods and exception handling

Separate conversion errors from valid numeric values.

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Java recursion and bounded factorial

Use a base case and validate the representable range.

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Java variables, types, and casting

Declare typed variables and understand integer division, overflow, and conversions.

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Java arrays and strings

Work with fixed-size arrays, common String methods, and the difference between == and equals.

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Java method overloading, varargs, and pass by value

Declare several methods with the same name and see what a method can and cannot change.

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Java constructors and encapsulation

Initialize private fields and validate changes through methods.

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Java inheritance and method overriding

Use a superclass reference to call subclass behavior.

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Java interfaces and composition

Depend on a contract and inject a collaborating object.

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Java abstract classes and enums

Define a shared base with an abstract method, and a fixed set of constants with fields.

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Java generics and bounded types

Write one class and one method that work for many types while the compiler checks them.

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Java equals, hashCode, and toString

Define when two objects are equal so that they work correctly in sets and maps.

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Java ArrayList and generics

Use a resizable, type-checked sequence.

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Java binary search and interval bounds

Implement logarithmic search on an ascending array.

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Java stacks and balanced brackets

Use a stack to check that brackets are properly nested.

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Java ArrayDeque as a queue

Choose queue operations with explicit empty-queue behavior.

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Java maps, sets, and duplicate counting

Track counts and distinct values with separate collection roles.

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Java singly linked lists

Build a list of nodes by hand, insert at the front and the back, and reverse it.

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Java binary search trees

Insert values into a tree that keeps smaller values on the left, and traverse it in sorted order.

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Java sorting: insertion sort, merge sort, and comparators

Implement two sorts by hand and sort objects with a Comparator.

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Java priority queues and heaps

Always remove the smallest (or largest) item, and find the k largest values.

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Java: counting operations to see growth rates

Count loop iterations instead of timing them to compare linear, quadratic, and logarithmic growth.

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Java: amortized cost of a growing array

Show that doubling a backing array makes append cost O(1) on average even though some appends copy everything.

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Java: a hash join and why it beats a nested loop

Join two collections by building a hash table on one side and probing it with the other.

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Java: an ordered index with TreeMap

Use a sorted map the way a database uses an ordered index to answer range and nearest-key queries.

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Java: simulating round-robin CPU scheduling

Rotate jobs through a ready queue with a fixed time slice and record when each one finishes.

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Java: mutual exclusion with synchronized

Protect a shared counter from lost updates when two threads increment it.

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Java: a TCP echo server on the loopback interface

Open a server socket on an ephemeral port and connect to it with a client socket in the same program.

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Java: IPv4 addresses, masks, and CIDR blocks

Compute the network address, broadcast address, and host count of a subnet with bitwise operations.

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Java: testing a method with a tiny test runner

Check normal cases, boundaries, and error cases, and report which ones pass.

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Java: strategy and observer with interfaces and lambdas

Swap behavior behind an interface and notify listeners without coupling the sender to them.

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Java: SHA-256 hashing for integrity

Compute a SHA-256 digest with MessageDigest and see that a tiny change produces a completely different value.

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Java: storing passwords with a salt and PBKDF2

Derive a password hash with a random salt and many iterations, then verify a login attempt.

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Java: splitting work across a thread pool

Divide a sum into chunks, run them on an ExecutorService, and combine the Future results.

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Java: parallel streams and CompletableFuture

Count items with a parallel stream and combine two asynchronous results.

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Java: breadth-first search for a shortest path

Search a grid with a queue to find the fewest moves from the start to the goal around walls.

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Java: game-tree search with minimax (negamax)

Search every move in a take-away game to find which positions are winning for the player to move.

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Java: propositional entailment by model checking

Enumerate every truth assignment to decide whether a knowledge base entails a query.

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Java: forward chaining with if-then rules

Repeatedly apply rules whose conditions are known until no new facts can be derived.

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Java: linear regression with gradient descent

Fit a straight line to data by repeatedly stepping the weights against the gradient of the squared error.

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Java: k-nearest-neighbors classification

Classify a point by letting its k closest training points vote.

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Java: training a perceptron to learn AND

Update the weights of a single neuron with the perceptron rule until it classifies all four inputs correctly.

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Java: a two-layer network that computes XOR

Combine two hidden neurons so that a network solves the problem a single perceptron cannot.

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Java: filtering an image with a convolution kernel

Slide a 3×3 averaging kernel over a small grayscale image to smooth it.

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Java: finding edges with the Sobel operator

Estimate the horizontal intensity change at each pixel and mark strong edges.

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