AI Generated

Java modifiers are keywords that are used to modify classes, methods, variables, and other elements in Java programming. They provide additional information or restrictions on the elements they modify.

There are several types of Java modifiers:

1. Access Modifiers: These modifiers determine the accessibility of classes, methods, and variables. The access modifiers in Java are public, protected, private, and the default (no modifier).
2. Non-Access Modifiers: These modifiers provide additional functionalities or restrictions. Some commonly used non-access modifiers include final, static, abstract, synchronized, and volatile.

• final indicates that a class cannot be inherited, a method cannot be overridden, or a variable cannot be reassigned.
• static indicates that a method or variable belongs to the class itself, rather than to an instance of the class.
• abstract indicates that a class cannot be instantiated and is meant to be subclassed.
• synchronized is used to control the access to shared resources by multiple threads.
• volatile is used to indicate that a variable may be modified asynchronously by multiple threads.

Modifiers play a crucial role in defining the behavior and accessibility of Java elements and help in code organization and security.

• public vs private → to support encapsulation of data
• static → For entities defined inside classes that exist without creating objects of the class.
• final → For values that cannot be changed.
• These Modifiers can be applied to classes, instance variables, and methods.

public vs private

• Used for faithful implementation of encapsulation.
  • Typically instance variables are private.
  • Methods to query (accessor) and update(mutator) the state are public.
• Can private methods makes sense? YES

  • Example: a Stack Class

    public class Stack{
    	private int[] values;  // array of values
    	private int tos;  //top of stack
    	private int size; // values.length
    
    	/* Constructors to set up values array */
    
    	public void push(int i){
    		...
    	}
    
    	public int pop(){
    		...
    	}
    
    	public boolean is_empty(){
    		return (tos == -1);
    	}
    }
    

  • Data stored in a private array

  • Public methods to push , pop, query if empty

  • push() needs to check if stack has space.

    public void push(int i){
    	if (tos < size){
    		values[tos] = i;
    		tos = tos + 1
    	}
    	else{
    			//Deal with stack overflow
    	}
    }
    

  • Deal gracefully with stack overflow

    • private methods invoked from within push() to check if stack is full and expand storage.

      

static