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Type Casting

When we assign a value of one type to a variable of another type, type casting performed.

  • Automatic conversions casting
  • Incompatible type casting

Automatic conversions casting

If the two types are compatible and the destination type is larger than the source type, this is automatic casting.

Incompatible type casting

To create a conversion between two incompatible types, you must use a cast. It is simply an explicit type conversion, general form:

(target-type) value

Arrays

An array is a group of like-typed variables, commomly reffered by a common name. It may has one or more dimensions with elements accessed by their index.

  • One-Dimentional Arrays

An array is specifically a list of like-typed variables. Simply general form:

type var-name[];

array-var = new type[size];

OR

type var-name[] = new type[size];

  • Multidimensional Arrays

Multidimentional arrays are implemented as arrays of arrays. Like:

type name[][] = new type[][]; (2D)
type name[][][] = new type[][][]; (3D)
.
.
.

Class & object

class basically defines a new data type, a class is the template for an object & object is instance of class.

class Syntax:

class classname {
    //body
}

object Syntax:

class-name object-name = new class-name();

Methods

Method Syntax:

type name(parameter-list) {
    //body of method
}

Constructors

Constructor initializes an object immediately upon creation. It has the same name as the class.

Syntax:

class class-name {
    class-name(parameter-list) {
        //body
    }
}

Recursion

Recursion is the process of defining something in terms of itself, it allows a method to call itself. Use if statement with recursion otherwise method will never terminate.

Variable-Length Arguments

Syntax:

data-type ... variable-name

Thus, VarArgs are specified by three periods(...). This syntax tells the compiler that variable number of arguments will be used, these args will be stored in an array referred to var-name.

Class Member Access

Category Private No Modifier Protected Public
Same class Yes Yes Yes Yes
Same package subclass No Yes Yes Yes
Same package non-subclass No Yes Yes Yes
Different package subclass No No Yes Yes
Different package non-subclass No No No Yes

Exceptions

Unchecked Exceptions: exceptions need not to be included in any method's throws list.

Checked Exceptions: exceptions that must be included in a method's throws list if that method can generate one of these exceptions & does not handle it itself.

Unchecked Exceptions

  • ArithmeticException
  • ArrayIndexOutOfBoundsException
  • ArrayStoreException
  • ClassCastException
  • EnumConstantNotPresentException
  • IllegalArgumentException
  • IllegalCallerException
  • IllegalMonitorStateException
  • IllegalStateException
  • IllegalThreadStateException
  • IndexOutOfBoundsException
  • LayerInstantiationException
  • NegativeArraySizeException
  • NullPointerException
  • NumberFormatException
  • SecurityException
  • StringIndexOutOfBoundsException
  • TypeNotPresentException
  • UnsupportedOperationException

Checked Exceptions

  • ClassNotFoundException
  • CloneNotSupportedException
  • IllegalAccessException
  • InstantiationException
  • InterruptedException
  • NoSuchFieldException
  • NoSuchMethodException
  • ReflectiveOperationException