Category Archives: Internet Technology

java tutorial: Java exception

A java exception is an event that occurs during the execution of a java program that disrupts the normal flow of instructions. Continue reading

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java tutorial: java 8 Lambda built-in functional interfaces

Java 8 functional interface: Function : R apply(T t), Supplier : T get() , Predicate : boolean test(T t) , Consumer : void accept(T t) Continue reading

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IntelliJ IDEA utility plugin

IntelliJ IDEA is an excellent Java IDE, with the help of excellent IDEA plugins, we can greatly improve efficiency in daily development. Continue reading

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MySQL tutorial: mysql inner, left, right, full join explained

Mysq joins two table query, roughly divided into inner join, full join (outer join), right join, and left join. Continue reading

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MySQL tutorial: mysql round() function

MySQL ROUND() is a mathematical function that rounds Numbers to a specified number of decimal places. Continue reading

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How to remove directories in linux/unix

To remove/delete directories (folders), we can use the rm command and the rmdir command. Continue reading

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java tutorial: three ways to generate random numbers in Java

Java random number have three ways: java.lang.Math.Random, java.util.Random, java.util.concurrent.ThreadLocalRandom Continue reading

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MySQL tutorial: mysql group by count percentage

Mysql group by count percentage, you can count the proportion of certain conditions in the total amount of data. Continue reading

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java tutorial: java 8 lambda expression example

Lambda expressions are a simplification of anonymous inner classes, a functional programming idea that makes code look cleaner. Continue reading

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MySQL tutorial: mysql concat() function

The MySQL CONCAT function accepts one or more string parameters and concatenates them into a string. Continue reading

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java tutorial: install Java JDK and Maven on Mac

Install Java JDK and Maven on mac os: 1) Download and install files from the official website; 2) Install using homebrew package manager. Continue reading

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list directory with ls command in linux/unix

In linux, with the ls command -d option, you can only list the directories of the current directory, not recursively. Continue reading

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What command is linux ll?

Linux ll is not a command provided by the linux system. It is usually the command alias we set. Generally, the ls -l command is set to ll. Continue reading

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Sort files or folders by size with ls command in linux/unix

The Linux ls -S option can be sorted by size from largest to smallest, or the ls -rS option can be sorted by size from smallest to largest. Continue reading

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How to recover deleted files in Linux

Linux recover deleted files, we can use the debugfs command. It can be used to examine and change the state of an ext2, ext3, or ext4 file system. Continue reading

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