Interfaces and abstract classes both provide a framework for future specific classes while also enforcing certain criteria to be met, but they do it in different ways.

1. **Interface**: An interface is a contract that defines a set of methods that the implementing class must have. It can't have any state or behavior, it's effectively a 100% abstract class. You can implement multiple interfaces, which offers a form of multiple-inheritance.

When to use: Use interfaces when you want to define the role that other classes should play, regardless of where they sit in the class hierarchy. Also, use when your blueprint needs to be implemented by classes which are not related to each other (i.e., not from the same class tree).

2. **Abstract Class**: An abstract class, on the other hand, provides a default behavior that can be shared among multiple classes. You can define fields (state) and concrete methods (behavior) in an abstract class. An abstract class can carry partially implemented methods. However, you can only extend one abstract class, due to Java's single inheritance model.

When to use: Use abstract classes when you have a clear, hierarchical structure and when you need to provide common behavior and/or default state that subclasses can inherit or override.

Remember, the choice between abstract classes and interfaces isn't just about technical differences, but also about expressing your design intent.

In Java, the `static` keyword is used in the context of a class, rather than an instance of a class. It pertains to members of a class, specifically variables and methods.

1. `Static` Variable: A static variable is common to all instances (or objects) of the class because it is a class level variable. This means there is only one copy of the static variable, regardless of how many instances of the class exist. So if you modify the value of the variable in one instance, the change is reflected in all other instances.

2. `Static` Method: Like static variables, static methods are also tied to the class itself, not any particular instance of it. Consequently, you can call a static method without creating an instance of the class. They can only manipulate static variables and can't interact with instance variables.

As for when to use it: If you have a variable that's not tied to an instance of a class and its value is consistent across all instances, it should be made static. This can improve space efficiency because only a single copy of the variable exists. Similarly, any function that doesn't use instance variables can be made static.

Example:

```java
public class Car {
static int numberOfCars = 0; // This is a static variable

public Car() {
numberOfCars++; // This will increase for every new Car object created
}

static void displayCarCount() { // This is a static method
System.out.println("Number of cars: " + numberOfCars);
}
}
```

In this example, `numberOfCars` is a static variable that increments each time a new `Car` object is created. `displayCarCount()` is a static method that displays the current count of cars. Both are tied to the Car class, not any specific instance of Car. We can call `displayCarCount()` without creating a Car object:

```java
Car.displayCarCount(); // prints "Number of cars: 0"
```

To delete a branch both locally and remotely in Git, you follow these steps:

Firstly, you'll want to delete the local branch. To do that, use the `-d` flag (short for --delete). In your terminal, input:

```bash
git branch -d branch_name
```

Replace "branch_name" with the name of your specific branch. This command will delete it if it has been fully merged with its upstream branch.

If you get an error saying the branch is not fully merged and you are certain you want to delete it anyway, use `-D` flag instead:

```bash
git branch -D branch_name
```

Secondly, to delete the branch on the remote, use:

```bash
git push origin --delete branch_name
```

The `--delete` flag instructs Git to remove the remote branch. "origin" is a typical name for your remote repository, replace it with your remote's name if different.

Finally, to confirm deletion, you can use the command:

```bash
git fetch --all --prune
```

The `--all` flag updates all remotes, and the `--prune` option removes any remote tracking branches which no longer exist on the remote. You can also check with `git branch -a` which will list all branches.

Remember to always ensure you have merged any changes you want to keep before deleting a branch.

Firstly, ensure that you have finished all of your work on the branch and safely merged it into the main branch if needed, as you will not be able to recover it once it is deleted.

**To delete the branch locally:**

Use the command:

```
git branch -d branch_name
```

The `-d` option will delete the branch only if it has already been fully merged in its upstream branch. If you want to force delete it regardless of its merged status, use `-D` instead.

**To delete the branch remotely:**

Use this command:

```
git push origin --delete branch_name
```

This tells `git` to push a deletion of `branch_name` to the `origin` remote. This is the same as:

```
git push origin :branch_name
```

The `:` before the branch name indicates to `git` that you want to push nothing into `branch_name` on `origin`, effectively deleting it.

Remember to replace `branch_name` with the actual name of your branch.

Just be certain when deleting branches, especially remotely, since it's a destructive operation that can't be undone. Always double-check your branch name and make sure your work is secured somewhere else (like in another branch or in the main branch) before deleting.

`git fetch` and `git pull` are both commands used to download new data from a remote repository. However, they serve different purposes and aren't interchangeable.

1. `git fetch`: This command brings your local copy of the remote repository up to date. It grabs any data from the target remote branch that does not already exist in your current branch. Importantly, it does not merge any of this new data into your working files. The primary use case for git fetch is if you want to see what's happened in the remote repository since your last pull without making any changes to your own files.

2. `git pull`: This command, on the other hand, does the job of both `git fetch` and `git merge`. It updates your current HEAD branch with the latest changes from the remote server. This means `git pull` not only downloads new data, but it also directly integrates these changes into your current working copy files. This has the potential to overwrite local changes.

In general, if you simply want to view the updates from the remote repository without changing your files, use `git fetch`. If you wish to download the latest data and integrate it into your project, use `git pull`. For safety, especially when working in a team, preferring `git fetch` followed by `git merge` might be a good approach to avoid overwriting local changes.

`git fetch` and `git pull` are both commands used to update your local repository with updates from a remote repository, but they operate differently.

- `git fetch` only downloads new data from a remote repository - but it doesn't integrate any of this new data into your working files. Fetch is great for getting a fresh view on all the things that happened in a remote repository.

- `git pull`, in contrast, is used with a different intent. This command is used to bring your repository up to date with the latest from the remote repository. It is equivalent to `git fetch` followed by `git merge`. In other words, `git pull` does a `git fetch` followed by a `git merge`.

When in doubt, simply do a `git fetch` to see what's changed. Then if you agree with those changes, you can do a `git merge` (or `git pull` to do both at same time).

"git push origin master" is a command that sends the commits you have made on your 'master' branch to the 'origin' remote repository.

Let's break it down:

1. 'git': Git is a version control system that lets you manage and keep track of your source code history.

2. 'push': This is a command in Git that sends your changes to the central repository. It's essentially the command that uploads your code to the repository.

3. 'origin': This is the default name Git gives to the server where your repository was cloned from. It's essentially a shorthand name for the remote repository's URL.

4. 'master': This is the default branch name in Git till version 2.27.0. However, since Git version 2.28.0, the default branch name is 'main'. It's where all the development usually happens and from where new branches are often created.

So essentially, when you say "git push origin master", you are saying "take my code from the 'master' branch and send it to the 'origin'" - which is your central repository.

Remember, before pushing changes, you should have pulled any changes from the remote repository to ensure you're not overwriting work. This is achieved with 'git pull origin master'.

`git push origin master` is a command that pushes the commits you have done on the 'master' branch of your local repository to the 'origin' remote repository.

Here's a breakdown:

1. `git`: This is the command-line tool that interacts with Git, a powerful version control system.

2. `push`: This is a command that tells git to push your commits to the remote repository. In other words, it uploads your changes to the remote repository.

3. `origin`: This is the default alias that Git has given to the remote repository where you cloned from.

4. `master`: This is the default main branch name for a git repository.

So, in a nutshell, this command is transmitting all of the commits on your local 'master' branch which are not yet on 'origin' to that location, making your changes available to all team members connected to the 'origin' repository. You are essentially syncing your local repository with the remote repository.

"git push origin master" is a command in Git that uploads the content of your local repository (the changes you've made) to the remote repository.

"git" is the tool you're using.

"push" is the command to transfer your commits from the local repository to the remote repository.

"origin" is the default name Git gives to the server where you cloned the repository from. It’s your project’s main repository, usually on a server.

"master" is the main branch in your project.

So "git push origin master" is content you've staged, committed, and are now telling Git to put that in your master branch on your origin. If everything is working correctly, your changes will now be visible in the origin/master branch.

Neptune, as a planet, doesn't have weight because weight depends on the gravitational field which varies by location. However, it has mass which is constant and equals approximately 1.024 × 10^26 kg. In weight, this would translate to approximately 1.14 x 10^28 pounds when considering Earth's gravity. However, this weight has no meaningful context outside an environment with gravity, like Earth. Neptune's mass is a more reliable and significant measure.