Thread: What is the purpose for declaring things private.

To prevent outside direct access. By forcing the use of setter/getter methods, you can make a variable read-only from outside of its class (you have a public getter but no public setter), you can completely hide the existence of variables from outside a class (no public setters or getters), or you can force a specific means of modifying a variable.
For example, if you had a variable which you wanted to make sure was always bounded between 5 and 50, you could write a setter like this:

private int var;
 
public setVar(int value) {
	if(value<5) {
		var = 5;
	}
	else if(value>50) {
		var = 50;
	}
	else {
		var = value;
	}
}

This ensures the restrictions are ALWAYS guaranteed when an outside class attempts to modify the variable, and you don't have to check the restriction everywhere else in the code where you intend on using the variable.

Basically, there are a lot of advantages to forcing the use of setters/getters instead of allowing other classes free-roam with the variables. For more information, research Encapsulation: What is Encapsulation in Java and OOPS with Example

Private access modifier is the most restrictive access level. Class and interfaces cannot be private.
Example:
public class Logger {
private String format;
public String getFormat() {
return this.format;
}
public void setFormat(String format) {
this.format = format;
}
}

there's no way for other classes to retrieve or set the format varable directly.

Nijan.G

When I hear this question I think of the Far Side comic where a passenger on a plane finds a switch on the armrest labelled "Wings stay on/Wings fall off"