Ben Chuanlong Du's Blog

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String in Java

Comments

  1. String is a immutable class in Java. Extensive operations on strings (e.g., + in a big loop) is usually very slow before Java 7 (the + operator is optimized by the compiler automatically starting from Java 7). To avoid this problem (in older versions of Java), you can use the StringBuilder

BufferedReader in Java IO

Comemnt

  1. The methods BufferedRead.readLine and BufferedRead.lines are very helpful for reading text Files.

public String BufferedRead.readLine

Reads a line of text. A line is considered to be terminated by any one of a line feed ('\n'), a carriage return ('\r'), or a carriage return followed immediately by a linefeed.

public Stream\<String> BufferedRead.lines

Returns a Stream, the elements of which are lines read from this BufferedReader. The Stream is lazily populated, i.e., read only occurs during the terminal stream operation. The reader must not be operated on during the execution of the terminal stream operation. Otherwise, the result of the terminal stream operation is undefined.

Assert in Java

  1. Avoid using assert in Java production code as assertion is not turned on by default. Throw exception instead (since assert is just a syntax sugar of throwing exceptions).

The most important thing to remember about assertions is that they can be disabled, so never assume they'll be executed.

Therefore keep the followings things in mind when using assertions:

Exceptions in Java

Things on this page are fragmentary and immature notes/thoughts of the author. Please read with your own judgement!

  1. You can suppress warnings of unchecked exceptions by using 

    SuppressWarnings("unchecked")

    but generally speaking, you cannot suppress warnings of checked exceptions.

  2. You can use more than one catch blocks if necessary …

Get Resources in Java

Things on this page are fragmentary and immature notes/thoughts of the author. Please read with your own judgement!

  1. getResource and getResourceAsStream tries to find files in the resources directory under src/main/resources or src/test/resources (depending on whether you are running the application or tests for the …

A JNI Error Has Occured

Things on this page are fragmentary and immature notes/thoughts of the author. Please read with your own judgement!

Error Messages

Error: A JNI error has occurred, please check your installation and try again

Caused by: java.lang.ClassNotFoundException: org.apache.spark.sql.SparkSession

Cause

Some dependencies (Spark in this …