Posts (238+)

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June 2026

Linux xargs:Turn Lists into Command Arguments

Hands-on xargs recipes for everyday work — feed find and grep into commands, batch safely, and place arguments where they belong.

Java

HashSet and LinkedHashSet:Unique Elements, With or Without Encounter Order

Use HashSet for uniqueness and LinkedHashSet when uniqueness still needs insertion order — both are HashMap wrappers, and neither is a sorted set.

Data Structures

Heaps:Priority in O(log n) Without Sorting the Whole Collection

A binary heap is a complete tree in an array that keeps the next-best element at the root. Min vs max, PriorityQueue in the JDK, and why you will hear Fibonacci heap without implementing one.

Java

ArrayList:The Default List and When Growth Bites

Use ArrayList as the default List — amortized append, O(1) get, ensureCapacity, and the fail-fast iterator — and know when growth copies the whole array.

Data Structures

B-Trees:Wide Nodes for Disk (and Why Databases Do Not Use BSTs)

A B-tree packs many keys per node so one disk page is one hop. Why databases and filesystems use this shape, and how B+ trees keep values in the leaves.

Linux

Linux journalctl:Query the systemd Journal

Hands-on journalctl recipes for everyday work — filter by unit, severity, time range, and boot, then read the results with confidence.

Java

Map:Keys, Values, and the Views That Stay in Sync

Use Map as mappings, not a Collection — get/put, compute and merge, and the keySet/values/entrySet views that write through to the same storage.

Data Structures

Red-Black Trees:The Shape Behind `TreeMap` and `TreeSet`

A red-black tree is a BST painted with color rules that keep height logarithmic without AVL’s strict balance. Why TreeMap and TreeSet use this shape.

Java

Queue and Deque:Ends, Not Indexes

Use Queue and Deque when the job is the ends — offer/poll versus add/remove, exception versus special value, and why indexes are the wrong primitive.

Data Structures

AVL Trees:Height Balance When You Need Strict Guarantees

An AVL tree is a BST that rebalances on insert and delete so height stays O(log n). Balance factors, rotations, and when the extra strictness is worth it versus red-black.