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Java Singleton Methods not Working


Java Singleton Methods not Working

By : user2956150
Date : November 22 2020, 10:54 AM
To fix this issue Your issue is that method calls in Java have to be in a method. So the issue you're having actually has little to do with the Singleton pattern at all, it's that you're trying to make a call in the body of a class, rather than a method. If you tried to compile the following you'd have the same error:
code :
public class HelloWorld{
    System.out.println("Hello, World!"); //Err
}
public class DataCore {

    // Singletons Tests - static
    static DCTest test;

    //Called when the DataCore class is loaded.
    static{
        test = DCTest.getInstance();
        test.setInt(0);
    }
}
public class DataCore {

    // Singletons Tests - nonstatic
    DCTest test;

    public DataCore(){
        test = DCTest.getInstance();
        test.setInt(0);
    }
}


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Singleton v/s class with static members & methods in Java

Singleton v/s class with static members & methods in Java


By : Qpeed
Date : March 29 2020, 07:55 AM
hope this fix your issue Collections.emptySet() is a typical example of a singleton that can't be implemented as a static class since, obviously, its goal is to be an instance of the java.util.Set interface. It's not costly to create, but it would be stupid to create a new instance each time an empty set is needed, since the unique instance can be reused.
iOS CoreLocation & Singleton pattern: Delegate methods not working

iOS CoreLocation & Singleton pattern: Delegate methods not working


By : Tony.L
Date : March 29 2020, 07:55 AM
hop of those help? I am creating a CLLocationManager singleton to be used by other objects in my app. For some reason when I call , I made my Core location singleton to be the delegate itself
code :
#pragma  mark - CLLLocation manager delegate
-(void) locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation   *)newLocation fromLocation:(CLLocation *)oldLocation
{
    self.currentLocation = newLocation;
}
@property (strong, nonatomic)CLLocation *currentLocation;
- (void)setCurrentLocation:(CLLocation *)currentLocation
{
    if (!_currentLocation) {
    _currentLocation = [[CLLocation alloc] init];
}
_currentLocation = currentLocation;
[[NSNotificationCenter defaultCenter] postNotificationName:@"did update location" object:nil];
 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updateLocation) name:@"did update location" object:nil];
 [self.locationManager startUpdatingLocation];
Java order of class fields and methods in singleton

Java order of class fields and methods in singleton


By : Lance Tipton
Date : March 29 2020, 07:55 AM
Hope this helps You have to understand what is going on when a class is being created. When a class is created, its static members are also created, line by line.
I think the real issue is that you declared SomeDataSource as static, when it should not be. However, to explain what is causing the issue, lets keep looking at it.
code :
private static SomeDataSource sDS = null;
private static SomeConnectionPool sCP = new SomeConnectionPool ();
public class SomeConnectionPool
{
   private static final Logger log = Logger.getLogger (SomeConnectionPool.class.getName());
   private static SomeDataSource sDS = new SomeDataSource (config);
   private static SomeConnectionPool sCP = new SomeConnectionPool ();

   private SomeConnectionPool ()
   {
     // Configure DataSource, connect to DB
   }
public class SomeConnectionPool
{
   private static final Logger log = Logger.getLogger (SomeConnectionPool.class.getName());
   private static SomeConnectionPool instance = new SomeConnectionPool ();
   private SomeDataSource sDS = null;

   private SomeConnectionPool ()
   {
     // Configure DataSource, connect to DB
      this.sDs = new SomeDataSource (config);
   }
   public static SomeConnectionPool getInstance ()
   {
     return instance;
   }
   public SomeDataSource getDataSource ()
   {
      return this.sDs;
   }
Java: when would I ever want to use static methods when I can use a singleton instead?

Java: when would I ever want to use static methods when I can use a singleton instead?


By : Queue
Date : November 24 2020, 05:47 AM
Hope that helps As with all questions of this nature, use the right tool for the job. Use a singleton when your class represents an object that there can be only one of. Use static methods when your methods are appropriate for the class they are members of but do not rely on a specific instance of that class.
In general, use your best judgment. Go for clean, precise, maintainable code, keeping the overall big picture in mind.
How to call methods within Java Singleton enum constructor?

How to call methods within Java Singleton enum constructor?


By : alkahf
Date : March 29 2020, 07:55 AM
Does that help This is because INSTANCE is declared before name, so it is created and initalized before name is initialized.
This works:
code :
public enum MyClass{
    INSTANCE;
    private static final String name = "Hello";

    MyClass() {
        test();
    }

    private static void test(){
        String name1 = name + "World";
        System.out.println(name1);
    }
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