java - Read For Learn

How do I instantiate a Queue object in java?

A Queue is an interface, which means you cannot construct a Queue directly. The best option is to construct off a class that already implements the Queue interface, like one of the following: AbstractQueue, ArrayBlockingQueue, ArrayDeque, ConcurrentLinkedQueue, DelayQueue, LinkedBlockingQueue, LinkedList, PriorityBlockingQueue, PriorityQueue, or SynchronousQueue. An alternative is to write your own class which implements the necessary Queue interface. It is not needed except in those rare cases where you wish to … Read more

FtpClient storeFile always return False

The exact failure message can be found by calling FtpClient#getReplyCode(). From that page (my emphasis): Immediately after connecting is the only real time you need to check the reply code (because connect is of type void). The convention for all the FTP command methods in FTPClient is such that they either return a boolean value or … Read more

How can I convert integer into float in Java?

You just need to cast at least one of the operands to a float: or or (unnecessary)

hat is the purpose of flush() in Java streams?

From the docs of the flush method: Flushes the output stream and forces any buffered output bytes to be written out. The general contract of flush is that calling it is an indication that, if any bytes previously written have been buffered by the implementation of the output stream, such bytes should immediately be written to their intended destination. … Read more

Encrypt Password in Configuration Files?

A simple way of doing this is to use Password Based Encryption in Java. This allows you to encrypt and decrypt a text by using a password. This basically means initializing a javax.crypto.Cipher with algorithm “AES/CBC/PKCS5Padding” and getting a key from javax.crypto.SecretKeyFactory with the “PBKDF2WithHmacSHA512” algorithm. Here is a code example (updated to replace the less secure MD5-based variant): One problem remains: Where … Read more

Encrypt Password in Configuration Files?

Variable might not have been initialized error

You declared them, but you didn’t initialize them. Initializing them is setting them equal to a value: You get the error because you haven’t initialized the variables, but you increment them (e.g., a++) in the for loop. Java primitives have default values but as one user commented below Their default value is zero when declared … Read more

Cannot instantiate the type Queue. Why is this?

This is my main method for a stacks/queues assignment. I keep getting an error with my queue, but not my Stack. The stack class seems to be working just fine. I’m completely stuck. It says “cannot instantiate type Queue”. Any help would be most appreciated!

What causes “‘void’ type not allowed here” error

If a method returns void then there is nothing to print, hence this error message. Since printPoint already prints data to the console, you should just call it directly:

java.net.SocketException: Connection reset

I am getting the following error trying to read from a socket. I’m doing a readInt() on that InputStream, and I am getting this error. Perusing the documentation this suggests that the client part of the connection closed the connection. In this scenario, I am the server. I have access to the client log files … Read more

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