🚀 Kotlin's Key Features #1

Saleemuddin Khan — Sun, 18 May 2025 13:58:14 +0000

🏹 Null Safety in Kotlin
Dodging the Null Pointer Exception, the Kotlin way🤓🤓

➤ Concept of Strict Null Safety in Kotlin
• Safe Call Operator ( ?. ) in Kotlin
• Elvis Operator ( ?: ) in Kotlin
• Not Null Assertion ( !! ) in Kotlin.

Kotlin allows to store “Null” values in a variable.
In Kotlin, the variables can be made of Null types by just adding a “?” symbol to the right side of the data type.
A nullable type variable means it can also hold “Null” as a value in it.
A non-nullable type variable means that it can not hold “Null” as a value in it.

The safe call operator is simply a question mark followed by a dot ( ?. )
The safe call operator in Kotlin, is one of the methods to impose “Null Safety Checks” on the nullable variables.
If the left-hand side of the operator is null, then it will return null value.
If the left-hand side of the operator is not null, then it will return the result of the right-hand side expression.

The elvis operator is represented by a question mark followed by a colon ( ?: )
The elvis operator in Kotlin, is one of the methods to impose “Null Safety Checks” on the nullable variables.
If the first operand is not null, then this operand will be returned by the elvis operator.
If the first operand is null, then second operand will be returned by the elvis operator.

The Not Null Assertion is represented by a double exclamation mark (!!)
The Not Null Assertion in Kotlin, is another tool to deal with nullity.
This operator explicitly casts nullable variables to non-nullable variables.

Arrays In Java

Saleemuddin Khan — Fri, 13 Dec 2024 11:12:10 +0000

Array introduction

An arrays is indexed collection of fix no of homogeneous elements.
The main advantage of arrays is we can represent usage no of values by using a single variable.so that read of the code ability improved. But the main disadvantage of arrays is fixed in size. That is once we create an arrays there is no chance of increasing or decreasing base on our requirement hence to use arrays concept compulsory we should know size in advance, which may not possible always.

Array declaration in java

One dimensional array declarations

int[] x;   Recommended --> Because Name is clearly Separated from Type

int []x;   These two ways also valid but first one is mostly use by java programmers
int x[];

int[6] x;  -> Invalid --> Because at the time of declaration we cant specify the size otherwise we will get compile time error.
int[]  x;  -> Valid   --> This is valid because just declare an array.

Two dimensional arrays

Two dimensional array declarations

int[][] x; Recommended --> Because Name is clearly Separated from Type

int [][]x; 

int x[][];

int[] []x;

int[] x[];

int []x[]; 

*/Also all these declaration is valid in java but mostly first one use by Java Programmers./*


Two dimensional array declarations mutiple variable in same line

int[] a,b;  
a-->1 both a and b is one dimensional array.
b-->1

int[] a[],b;
a-->2 a is two dimensional array.
b-->1 but b is one dimensional array.

int[] a[],b[];
a-->2 a is two dimensional array.
b-->1 b is also dimensional array.

int[] []a,b;
a-->2 a is two dimensional array.
b-->1 b is one dimensional array.

int[] []a,b[];
a-->2 a is two dimensional array.
b-->3 but b is three dimensional array.

int[] []a,[]b;     ---> Compile Time Error
int[] []a,[]b,[]c; ---> Compile Time Error

/*if you went specify dimension before the variable the facility is applicable only for first variable in a declaration. if you are try to apply remaining variable we will get compile time error./*

Three dimensional arrays

wo dimensional array declarations

int[][][] a; Recommended --> Beacuse Name is clearly Seprated from Type

int [][][]a;

int a[][][];

int[] [][]a;

int[] a[][];

int[] []a[];

int[][] []a;

int[][] a[];

int [][]a[];

int []a[][];

*/Also all these declaration is valid in java but mostly first one use by Java Programmers/*.

Array Creations in java

One dimensional array creations

Two dimensional array creations

Three dimensional array creations

Every array in java is an object only. Hence we can create arrays by using new operator.
a ,b,c,p,q,r,x,y,z → all is reference variable.

for every array type of corresponding class are available and these class are part of java.lang package and not available to programmer level.

Array Types → Corresponding Class Names

int[] → [I
int[][] → [[I
double[] → [D
short[] → [S
byte[] → [B
boolean[] → [Z
String[] → [java.lang.string;

At the time of array creation compulsory we should specify the size. otherwise we will get compile time error.

It is legal to have an array with size zero in java.

If you are trying to specify array size with some Negative int value then we will get Runtime exception “NagativeArraySizeException”

To specify array size allowed data type are byte,short,char,int.

Because byte → to ← short conversion is possible. short → to ← int conversion is possible. char → to ← int conversion is also possible.

long →to ← int conversion is not possible so when we try then it show compile time error.

conclusion → if you are try to specify any other type then we will get compile time error.

Array Maximum Size Allowed In Java

First Case →

The maximum allowed array size in java is “2147483647”.
which is the maximum value of int datatype.
Even in the first case we may get → RuntimeException → If Sufficient memory not available.

Second Case →

If we are try to assign 2147483648 size of our array then we get Compile time Exception → Integer Number is too large.
Because → In Java Array Support Maximum Integer Value As Size.
In Java Maximum Int datatype value is → “2147483647”.

Happy Coding...

DEV Community: Saleemuddin Khan

🚀 Kotlin's Key Features #1

Arrays In Java