Applications > Utilities > Activity Monitor.app, locate Docker or Docker Desktop, and if it’s not responding, select it and click Force Quit.
Fix Docker Suddenly Not Working on Mac
If your Docker on Mac was working fine but suddenly stops starting, this guide will help you fix it.
Important: This process will delete all your Docker containers.
Step 1: Force Quit Docker
Open Finder, navigate to
Step 2: Remove Docker Containers
Open Terminal and run the following command. This will delete all your Docker containers and reset the container files.
sudo rm -rf ~/Library/Containers/com.docker.*
Step 3: Edit Docker Settings
Open the Docker settings file in Terminal:
sudo nano ~/Library/Group\ Containers/group.com.docker/settings.json
Find the key
"filesharingDirectories" and remove all entries inside it, leaving it like this:
"filesharingDirectories": []
Step 4: Restart Docker
Go back to your Applications folder, locate Docker, and launch it. It may take a minute or so to fully start.
References
System Design resources
System design is a crucial skill for software engineers, especially in high-scale, production-level applications. Here are some of the best resources for learning system design, ranging from books to online courses and websites
Websites & Blogs
Key Topics to Focus On
As you explore these resources, here are some essential topics to focus on when learning system design:
Scalability: Horizontal vs. vertical scaling, sharding, partitioning, and load balancing.
Reliability: Fault tolerance, replication, consistency models (CAP theorem), and high availability.
Data Storage & Databases: SQL vs. NoSQL, data modeling, caching, and indexing.
Distributed Systems: Eventual consistency, distributed messaging, and microservices.
Performance: Latency, throughput, bottlenecks, and optimization techniques.
Security & Privacy: Authentication, authorization, encryption, and securing data in transit.
Design Patterns: Event-driven architecture, CQRS, and service-oriented architecture.
Following are some curated links to learn system design.
The System Design Primer is a popular open-source resource on GitHub, primarily designed to help software engineers prepare for system design interviews. It's created and maintained by Donne Martin and provides a comprehensive guide for understanding key concepts, patterns, and approaches related to designing large-scale systems.
Roadmap.sh is a popular open-source resource that provides interactive learning paths (or roadmaps) for developers and engineers. It’s designed to help people navigate the learning process and give them a clear, structured guide to becoming proficient in various areas of software development.
HelloInterview is a platform designed to help individuals prepare for technical interviews, particularly in the fields of software engineering and development. The website offers a variety of resources aimed at improving your interview skills, with a focus on coding challenges, system design, and behavioral interview questions
Another popular github repo for System design
Another very use full site to learn system design concepts. It also provides a quiz module to assert the knowledge.
ByteByteGo is an online platform created by Alex Xu, a software engineer, designed to help developers prepare for system design interviews
This site provides some example design of highly scalable systems
Summary
By leveraging these resources and focusing on core concepts like scalability, reliability, and performance, you can master system design and be well-prepared for both real-world projects and technical interviews. Please let us know if you have any other sources to be added in the article.
Table of Content
Getting this simple problem while importing Xgboost on Jupyter notebook
Sometimes when we try to import xgboost in Jupyter notebook it does not work and throws error. This page contains the step taken to solve the issue successfully.
Issue: Cannot import xgboost in Jupyter notebook
In this case it was a Jupyter note book that was installed locally on Mac.
Error: Following error seen in Jupyter notebook
XGBoost Library ({libname}) could not be loaded.
225 Likely causes:
226 * OpenMP runtime is not installed
227 - vcomp140.dll or libgomp-1.dll for Windows
228 - libomp.dylib for Mac OSX
229 - libgomp.so for Linux and other UNIX-like OSes
230 Mac OSX users: Run `brew install libomp` to install OpenMP runtime.
231
232 * You are running 32-bit Python on a 64-bit OS
Solution
Install libomp
Go to the terminal and install libomp with following command
brew install libompSummary
After installing libomp the import of Xgboost worked in Jupyter notebook. Please note that if we dont have brew installed we need to install brew first.
Table of Content
npm and npx
Both npm and npx are tools that come with Node.js, but they serve different purposes.
npm
Full Form: Node Package Manager
Purpose: npm is used for managing packages in Node.js projects. It helps you install, update, and
npm Commands
- remove packages, as well as manage project dependencies.:
- npm install
: Installs a package. - npm uninstall
: Removes a package. - npm update: Updates all packages to the latest versions.
- npm list: Lists installed packages and their versions.
npx
Full Form: Node Package Executor
Purpose: npx is used to execute binaries from Node modules or packages without needing to install them globally. It's especially handy for running CLI tools that are part of your project or that you don't want to install globally.
npx Commands
- npx
: Runs a command from a package. For example, npx create-react-app my-app will run the create-react-app command without needing to install it globally.
Example Scenario
If you want to start a new React project, you could use:
This command runs create-react-app without having it installed globally.
npx create-react-app my-appIf you wanted to install create-react-app globally for repeated use, you would use:
Bellow code uses npm to install create-react-app globally
npm install -g create-react-app
Summary
To run Node.js packages without having to install them globally, npx is very helpful. We can use it to run command-line interface (CLI) tools, run scripts, and carry out other operations.
Table of Content
How to find Hamming Weight in Java
Hamming weight of a number is the count of bits that are set to
1.
For instance:
- 1001 → Hamming weight = 2
- 100001111 → Hamming weight = 5
Using Simple Division and Remainder
Here we divide the number by 2 repeatedly until it becomes 0.
At each step, we check if the remainder is 1 (i.e., the least significant bit is set).
public static int hammingWeight(int n) {
int count = 0;
while (n != 0) {
if (n % 2 == 1) {
count++;
}
n = n / 2;
}
return count;
}Using Bit Masking
In this example, we use bit masking.
Since an
int in Java has 32 bits, we shift a mask bit and check each position with a bitwise AND.
public static int hammingWeightII(int n) {
int count = 0;
int mask = 1;
for (int i = 0; i < 32; i++) {
if ((n & mask) != 0) {
count++;
}
mask = mask << 1; // shift the mask
}
return count;
}Full Example
package ic.binary;
public class NumberOf1s {
public static void main(String[] args) {
int n = 5;
System.out.println("Number of 1 bits for " + n + " -> " + hammingWeight(n));
System.out.println("Number of 1 bits for " + n + " -> " + hammingWeightII(n));
n = 8;
System.out.println("Number of 1 bits for " + n + " -> " + hammingWeight(n));
System.out.println("Number of 1 bits for " + n + " -> " + hammingWeightII(n));
}
public static int hammingWeight(int n) {
int count = 0;
while (n != 0) {
if (n % 2 == 1) {
count++;
}
n = n / 2;
}
return count;
}
public static int hammingWeightII(int n) {
int count = 0;
int mask = 1;
for (int i = 0; i < 32; i++) {
if ((n & mask) != 0) {
count++;
}
mask <<= 1;
}
return count;
}
}Output of above program
Number of 1 bits for 5 -> 2
Number of 1 bits for 5 -> 2
Number of 1 bits for 8 -> 1
Number of 1 bits for 8 -> 1
Table of Content
Java OptionalInt example
OptionalInt allows us to create an object which may or may not contain an int value.
If a value is present, isPresent() will return true and getAsInt() will return the value.
Additional methods that depend on the presence or absence of a contained value are provided, such as orElse().
Other classes similar to OptionalInt are OptionalDouble, OptionalLong, and Optional.
These help us eliminate exceptions that occur due to the absence of a value at runtime.
The key is to first check if the Optional contains a value before trying to retrieve it.
OptionalIntExample
In this example, we return an OptionalInt from a Stream created from an integer array and finally return a value using the reduce() method.
If the value is present, then only we print it using getAsInt().
package javaexp.blogspot.stream;
import java.util.Arrays;
import java.util.OptionalInt;
public class OptionalIntExample {
public static void main(String[] args) {
int iarray[] = {9, 10, 11, 12, 15, 15, 25};
OptionalInt result = Arrays.stream(iarray)
.reduce((left, right) -> left);
if (result.isPresent()) {
System.out.println("First element of Array: " + result.getAsInt());
}
}
}
Summary
OptionalInt and other respective Optional classes help protect against
NullPointerException when trying to retrieve values from potentially null objects.
They provide a safer way to work with values that may or may not be present.
Table of Content
Bucket Sort in Java
In this article we will go through a simple implementation of Bucket Sort in Java.
What is Bucket Sort
Bucket Sort is a sorting algorithm that divides the input into several buckets. Once the buckets are populated with input data, they are sorted individually using another sorting mechanism. After sorting, the buckets are concatenated together to produce the final result.
Following is the pseudocode for Bucket Sort:
function bucketSort(array, k) is
buckets ← new array of k empty lists
Max ← the maximum key value in the array
Min ← the minimum key value in the array
Divisor ← (Max - Min) / (k - 1)
for i = 0 to length(array) do
insert array[i] into buckets[floor((array[i] - Min) / Divisor)]
for i = 0 to k do
Sort(buckets[i])
return concatenation of buckets[0] ... buckets[k]
Bucket Sort implementation in Java:
import java.util.*;
public class BucketSortExample {
public static void main(String[] args) {
int[] arr = {8, 4, 2, 10, 3, 1, 9, 6, 5, 7};
int numBuckets = 5;
bucketSort(arr, numBuckets);
System.out.println("Sorted array:");
for (int value : arr) {
System.out.print(value + " ");
}
}
public static void bucketSort(int[] arr, int numBuckets) {
if (numBuckets <= 0) return;
// create empty buckets
ArrayList> buckets = new ArrayList<>(numBuckets);
for (int i = 0; i < numBuckets; i++) {
buckets.add(new ArrayList<>());
}
distributeToBuckets(arr, numBuckets, buckets);
// sort each bucket
for (ArrayList bucket : buckets) {
Collections.sort(bucket);
}
// concatenate
int index = 0;
for (ArrayList bucket : buckets) {
for (int item : bucket) {
arr[index++] = item;
}
}
}
private static void distributeToBuckets(int[] arr, int numBuckets,
ArrayList> buckets) {
int min = Arrays.stream(arr).min().getAsInt();
int max = Arrays.stream(arr).max().getAsInt();
float diff = max - min;
float divisor = diff / (numBuckets - 1);
for (int value : arr) {
int index = (int) ((value - min) / divisor);
if (index >= numBuckets) index = numBuckets - 1; // safeguard
buckets.get(index).add(value);
}
}
} Complexity
The best case for Bucket Sort happens when the data is distributed evenly across buckets.
This uniform distribution minimizes the sorting inside buckets, leading to overall time complexity:
Best Case: O(n + k)
Average Case: O(n + k)
Worst Case: O(n²)
Space Complexity: O(n + k)
Best Case: O(n + k)
Average Case: O(n + k)
Worst Case: O(n²)
Space Complexity: O(n + k)
Summary
Bucket Sort is a distribution-based sorting method where input elements are distributed into buckets, and each bucket is sorted using another algorithm. The sorted buckets are then concatenated to form the final sorted output.
IntSummaryStatistics
IntSummaryStatistics provides different statistical data like max, min, average. This class is desinged to work with Java streams but can work with with out streams also.
Example
Following class shows an example of IntSummaryStatistics used with stream. It is used to print interesting information like max, min, average, sum and count.
And then the accept method is used to add a new integer to the previous data passed as the numStream.
public class IntSummaryStatisticsExample {
public static void main(String[] args) {
Stream<Integer> numStream = Stream.of(1, 2, 3, 4, 5);
IntSummaryStatistics summary = numStream.mapToInt(p-> p).summaryStatistics();
System.out.println("Max From the Data is " + summary.getMax());
System.out.println("Min From the Data is " + summary.getMin());
System.out.println("Average From the Data is " + summary.getAverage());
System.out.println("Sum From the Data is " + summary.getSum());
System.out.println("Count From the Data is " + summary.getCount());
//Add a new number to the stream
System.out.println("\n");
summary.accept(10);
System.out.println("Max From the Data is " + summary.getMax());
System.out.println("Min From the Data is " + summary.getMin());
System.out.println("Average From the Data is " + summary.getAverage());
System.out.println("Sum From the Data is " + summary.getSum());
System.out.println("Count From the Data is " + summary.getCount());
}
}
IntSummaryStatistics Example
Max From the Data is 5
Min From the Data is 1
Average From the Data is 3.0
Sum From the Data is 15
Count From the Data is 5
Adding number 10 to the data
Max From the Data is 10
Min From the Data is 1
Average From the Data is 4.166666666666667
Sum From the Data is 25
Count From the Data is 6
IntSummaryStatistics Example
Max From the Data is 5
Min From the Data is 1
Average From the Data is 3.0
Sum From the Data is 15
Count From the Data is 5
Adding number 10 to the data
Max From the Data is 10
Min From the Data is 1
Average From the Data is 4.166666666666667
Sum From the Data is 25
Count From the Data is 6
Conclusion
IntSummaryStatistics defined in java.util package and available since java 8 provides a way to calculate statistical information. It works with and with out stream.
How to convert Java Stream to List
Convert Java Stream to List
Following code show how to convert the stream intStream to list using collect.
// Converting Streams to Collection
Stream<Integer> intStream = Stream.of(1, 2, 3, 4, 5);
List<Integer> list = intStream.collect(Collectors.toList());
System.out.println(list); // prints [1, 2, 3, 4, 5]
#include
#include
dht DHT;
#define DHT11_PIN 7
void setup(){
Serial.begin(9600);
}
void loop(){
int chk = DHT.read11(DHT11_PIN);
Serial.print("Temperature = ");
Serial.println(DHT.temperature);
Serial.print("Humidity = ");
Serial.println(DHT.humidity);
delay(1000);
}
//#include
#define MQ2pin (0)
//https://robu.in/mq2-sensor-interfacing-with-arduino-gas-and-smoke-detection/
float sensorValue; //variable to store sensor value
void setup()
{
Serial.begin(9600); // sets the serial port to 9600
Serial.println("Gas sensor warming up!");
Serial.println("I can detect 300 - 10000ppm");
delay(20000); // allow the MQ-2 to warm up
}
void loop()
{
sensorValue = analogRead(MQ2pin); // read analog input pin 0
Serial.print("Sensor Value: ");
Serial.print(sensorValue);
Serial.println("");
delay(2000); // wait 2s for next reading
}
Extract content of .war file
A WAR file (Web Application Resource or Web application Archive) is a file used to distribute a collection of files and folders associated with web application. Sometimes we want to look inside the war file to know what files or folders are inside the war file.
Jar -xvf
jar with option -xvf will extract the content of the war file. Following command will extract the content of blogapp.war file into the current directory
jar -xvf blogapp.war
To extract the content of war file type the above command. For instance for a war file blogapp.war
we can use the command jar -xvf.
Conclusion
jar -xvf can be used to extract the content of jar file. This command will work in any platform with installed java.
HashMap computeIfPresent() method in Java with Examples
The computeIfPresent(Key, BiFunction) method of HashMap class is used to update value in a key-value pair in the map. If key does not exist then it does not do any thing.
Syntax
undefined
V computeIfPresent(K key,
BiFunction<? super K, ? super V, ? extends V> remappingFunction) Example
Following is an example of computeIfAbsent invocation and its results.
ComputeIfAbsentExample
package corejava.map;
import java.util.HashMap;
import java.util.Map;
public class ComputeIfPresentExample {
public static void main (String argv[]) {
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("Sunglass", 105);
map.put("Watch", 1501);
newline("Original Map");
map.forEach((a, b) -> {
System.out.println(a + " -> " + b);
});
map.computeIfPresent("Watch", (k,v) -> {return v + v;});
newline("After calling computeIfAbsent Map");
map.forEach((a, b) -> {
System.out.println(a + " -> " + b);
});
}
static void newline(String s) {
System.out.println("\n" + s);
};
}
Output of above program.
Original Map Watch -> 1501 Sunglass -> 105 After calling computeIfAbsent Map Watch -> 3002 Sunglass -> 105
Summary
computeIfPresent helps in writing more compact code and also make code more readable.
HashMap computeIfAbsent() method in Java with Examples
The computeIfAbsent(Key, Function) method of HashMap class is used to enter a new key-value pair to map if the key does not exist. If key exists then it does not do any thing.
Syntax
undefined
public V computeIfAbsent(K key, Function<? super K, ? extends V> remappingFunction)Example
Following is an example of computeIfAbsent invocation and its results.
ComputeIfAbsentExample
package corejava.map;
import java.util.HashMap;
import java.util.Map;
public class ComputeIfAbsentExample {
public static void main (String argv[]) {
Map<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "one");
map.put(2, "two");
map.put(3, "three");
map.put(4, "four");
map.put(5, "five");
newline("Original Map");
map.forEach((a, b) -> {
System.out.println(a + " -> " + b);
});
map.computeIfAbsent(6, k-> { return "six";});
map.computeIfAbsent(7, k -> "seven");
newline("After calling computeIfAbsent Map");
map.forEach((a, b) -> {
System.out.println(a + " -> " + b);
});
}
static void newline(String s) {
System.out.println("\n" + s);
};
}
Output of above program.
Original Map 1 -> one 2 -> two 3 -> three 4 -> four 5 -> five After calling computeIfAbsent Map 1 -> one 2 -> two 3 -> three 4 -> four 5 -> five 6 -> six 7 -> seven
Summary
computeIfAbsent helps in writing more compact code and also make code more readable.
Remove all entries in map by value
Java Map is a data structure that holds key->value pairs. In this article we will see how to delete all entries in the map by map values.
Using removeAll
removeAll() takes one argument a collection. And entries matching the passed collection will be removed from the original map
Using removeAll
Map<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "one");
map.put(2, "two");
map.put(3, "three");
map.put(4, "four");
map.put(5, "five");
map.put(6, "five");
newline("Original Map");
map.values().removeAll(Collections.singleton("five"));
newline("After removing values = five");
map.forEach( (a,b) -> {
System.out.println(a + " -> " + b);
});Output of above program.
Original Map 1 -> one 2 -> two 3 -> three 4 -> four 5 -> five 6 -> five 7 -> five After removing values = five 1 -> one 2 -> two 3 -> three 4 -> four
Using removeIf
removeIf
Map<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "one");
map.put(2, "two");
map.put(3, "three");
map.put(4, "four");
map.put(5, "five");
map.put(6, "five");
newline("Original Map");
//remove entries where value = five
map.values().removeIf("five"::equals);
newline("After removing values = five");
map.forEach( (a,b) -> {
System.out.println(a + " -> " + b);
});Output of above program.
Original Map 1 -> one 2 -> two 3 -> three 4 -> four 5 -> five 6 -> five 7 -> five After removing values = five 1 -> one 2 -> two 3 -> three 4 -> four
