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How to complie .java file in command line: 1.1. in Windows shell, if the classpath is not defined, we have a source file, BinarySearch.java in the folder ./javasrc/ch01_1/, use:
javac -cp ./\;./lib/algs4.jar javasrc/ch01_1/BinarySearch.javaor
javac -cp "./;./lib/algs4.jar" javasrc/ch01_1/BinarySearch.java
1.2. in Linux bash Same situation as 1.1.
`javac -cp "./:./lib/algs4.jar" javasrc/ch01_1/BinarySearch.java`
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How to run compiled .class file in command line: 2.1. in Windows shell, if the classpath is not defined, we have a compiled file, BinarySearch.class in the folder ./javasrc/ch01_1/, and 2 data files ./data/tinyW.txt and ./data/tinyT.txt for arguments, use:
java -cp ./\;./lib/algs4.jar javasrc/ch01_1/BinarySearch data/tinyW.txt < data/tinyT.txtor
java -cp "./;./lib/algs4.jar" javasrc/ch01_1/BinarySearch data/tinyW.txt < data/tinyT.txt
2.2. in Linux bash Same situation in 2.1.
`java -cp "./:./lib/algs4.jar" javasrc/ch01_1/BinarySearch data/tinyW.txt < data/tinyT.txt`
- SUMMARY of compiling and running using command line:
3.1. For
javacorjavaccommands,-cpdefines the class path, followed with a string of paths.
3.2. For cp string in Windows shell, paths are separated with ;. And cp string can be quoted or
not quoted, if not quoted, ; need be escaped: \;.
3.3. For cp string in Linux, paths are separated with :.
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Add Pycairo for 2d drawing in Python: install in python
pip install pycairo
install in anaconda
`conda install -c anaconda pycairo`
Home page is here
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How to input EOF "End Of File" in command line. In Windows shell, it is
Ctrl+ZIn Linux bash, its isCtrl+D -
How to create generic array in java There are Strong Typing and Weak Typing, we talk Weak Typing here
public class FixedCapacityStack {
private T[] a; private int N; public FixedCapacityStack(int capacity) { @SuppressWarnings("unchecked") T[] a = (T[]) new Object[capacity]; this.a = a; }}
6.1. You need annotation: @SuppressWarnings("unchecked"), 6.2. Create an array of object (new Object[capacity]) first, 6.3. Then, cast it to generic type, 6.4. casted generic array can not be directly assigned to instance variable, use a template variable to transfer.
- Immutable integer range
Java's implementation of
valueOf()retrieves a cached values if the integer isbetween -128 and 127, while Java constructs new objects for each integer outside this range.
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Allocate more memory and stack space for java VM 7.1. Increase memory The default setting of memory for JVM is typically 64MB. To increase memory allotted to Java, execut with:
java -Xmx200m Hello
where 200m means 200 megabytes.
7.2. Increase stack The default setting of stack for JVM is typically 128KB. To increase stack size, excute with:
`java -Xss200k Hello`
where 200k means 200 kilobytes.
And, it's possible to increase both the amount of memory and stack space by executing with:
`java -Xmx200m -Xss200k Hello`
- Java Assertion An assertion is a statement in Java which ensures the correctness of any assumptions which have been done in the program. When an assertion is executed, it is assumed to be true. If the assertion is false, the JVM will throw an Assertion error.
8.1. usage
`assert expression;`
`assert expression1 : expression2;`
8.2. turn on/off assertion in JVM, default is off. 8.2.1. for files
`java -ea filename` or `java -enableassertions filename`
`java -da filename` or `java -disableassertions filename`
8.2.2. for package run filename, only assertion in packagename will be enabled
`java -ea:packagename... filename`
8.2.3. for class run filename, only assertion in packagename.classname will be enabled
`java -ea:packgagename.classname filename`
- Linux StdDraw Error fix
In Linux, running StdDraw may get this error:
Exception in thread "main" java.lang.ExceptionInInitializerErrorCaused by: java.awt.HeadlessException:No X11 DISPLAY variable was set, but this program performed an operation which requires it.
To fix it, run this command:
`export DISPLAY=:0`
Where :0 would mean the first X server running. If you are running several X servers (for example Xvnc) on the target host, :0 may become :1 or another number, depending on X server configuration.
- Recomended vscode extension
- Better Comments: very nice colorized comments, all my comments are based on it.
- Bracket Pair Colorizer: help to identify bracket pairs.
- New cloned repositary cannot start running/debugging
For newly cloned repositary, pressing F5 to start running/debugging may get an error:
Error: Could not find or load main class XXXCaused by: java.lang.ClassNotFoundException: XXX
To fix it, add the line below to .vscode/settings.json, create the file/folder if it does not exist:
`{ "java.project.sourcePaths": ["./"] }`