Problem scenario
You run java commands but you get the error “/usr/bin/java no such file or directory.” What should you do?

Possible Solution #1
Reinstall Java.

Possible Solution #2
You may have deleted a linked file. To find the destination file, run this:

sudo find / -name java -type f

Based on the results,

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Problem scenario
You are using Eclipse for the first time. You try to to use Run, but you get an error message like this: “Unable to Launch The selection cannot be launched, and there are no recent launches.” Or you try to go to “Run configuration” and you have a prototype, but the “Run” button is grayed out. What should you do?

Solution
In the Run configuration section,

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Continue reading “How Do You Run Code in the Eclipse IDE?”

Problem scenario
You are getting an error such as “java.lang.OutOfMemoryError java heap space”

You have plenty of swap space available, but this error persists. The problem is as if nothing is using swap space you know exists. Why won’t your Java program or Maven build utilize the swap space that is available to it?

Possible solution #1 (for Maven builds)
Run a command like one of these (but uncomment the second one if you want to commit roughly 5 GB of memory to the maven build):

export MAVEN_OPTS=-Xmx512m
# export MAVEN_OPTS=-Xmx5120m

Now retry your mvn command.

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Problem scenario
You run Java programs on your Linux server. You want to view content of Java thread dumps. What should you do?

Solution
Prerequisites
Install Java if it has not already been installed. See this posting if you need assistance.

You may or may not want to learn more about what a Java thread is;

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Continue reading “How Do You Analyze Java Thread Dumps?”

Problem scenario
You want to accept user input with a Java program. How do you write such a program?

Solution
Here is the program:

import java.util.Scanner;

public class acceptChar {

public static void main(String[] args) {
System.out.println(“Please enter a character, then press enter: “);
Scanner in = new Scanner(System.in);
char letter = in.next().charAt(0);
System.out.println(letter);
}
}

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Continue reading “How Do You Write a Java Program to Accept a Character as Input and Do Something with It?”

Problem scenario
You want to pass an argument to another piece of code (e.g., a function in Java). How do you pass an array as a parameter to another portion of code?

Solution
Java only has methods — not functions (according to this posting).

This code (which should be called contInt.java) will pass a two-dimensional array called twoD to the method “coolp”.

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Continue reading “How Do You Pass an Array to a Method in Java?”