ACCESS MODIFIERS

                          access specifiers

Java provides a number of access modifiers to set access levels for classes, variables, methods and constructors. The four access levels are:Visible to the package. The default. No modifiers are needed.
Visible to the class only ( private ).
Visible to the world (public ).
Visible to the package and all subclasses protected .
 
Default Access Modifier - No keyword:
Default access modifier means we do not explicitly declare an access modifier for a class, field, method etc.
A variable or method declared without any access control modifier is available to any other class in the same package. The default modifier cannot be used for methods, fields in an interface.
 
Private Access Modifier - private:
Methods, Variables and Constructors that are declared private can only be accessed within the declared class itself.
Private access modifier is the most restrictive access level. Class and interfaces cannot be private.
Variables that are declared private can be accessed outside the class if public getter methods are present in the class.
 
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class Logger{
    private String format;  
    public String getFormat(){
        return this.format;
    }
    public void setFormat(String format){
        this.format = format;
    }
 }
 
Here, the format variable of the Logger class is private, so there's no way for other classes to retrieve or set its value directly.
So to make this variable available to the outside world, we defined two public methods: getFormat(), which returns the value of format, and setFormat(String), which sets its value.
 
Public Access Modifier - public:
A class, method, constructor, interface etc declared public can be accessed from any other class. Therefore fields, methods, blocks declared inside a public class can be accessed from any class belonging to the Java Universe.