These are lines of code that does not run (ctrl + / )
- Single line comment
// Single line comment - Multiple Line Comment
/** * Multi line comment * * line 2 of comment * */
-
Capital and small alphabets have different meaning in the language
-
All instruction/statement end with a semi-colon ( ; - Terminator )
System.out.println("Hello Arjun!!");
System.out.print("hello");
System.out.printf("%.5f", 123.45242);
System.out.println(String.format("%.4f", 12.34673637));| Data | Data Types |
|---|---|
| Numbers | int |
| Large Numbers | long |
| Decimal Numbers | float |
| Large Decimal Numbers | double |
| Character | char |
| Text | String |
| True / False | boolean |
Box that can store one value of a single data type
- It can contain alphabets, digits and special character _
- It can begin with alphabet or _
- It cannot contain spaces. camelCase, SentenceCase, under_score
- It cannot be a keyword (48 words)
- We cannot access a variable before creation
- There cannot be 2 variables with the same name in the same scope
Area in which the variable is accessible
- A variable is only accessible in its scope
- A variable is accessible in all the child scopes
int a = 20;
{
System.out.println(a);
{
System.out.println(a);
}
}
int a = 20;
{
int a = 10; // Error: Variable with the name a already exists
System.out.println(a);
}
{
int a = 10;
System.out.println(a);
}
{
int a = 20;
System.out.println(a);
} int a = 17;
int b = 4;
int s = a + b;
int d = a - b;
int m = a * b;
int q = a / b;
int r = a % b;
System.out.println(s);
System.out.println(d);
System.out.println(m);
System.out.println(q);
System.out.println(r);
double d1 = a;
double d2 = b;
double d = d1 / d2;
System.out.println(d);- numbers -
int - decimal number -
double
System.out.println(12344);
System.out.println(13/4);
int a = 12234273874848;
long l = 12234273874848L;
System.out.println(l);
double d = 14.456323637;
float f = 14.456323F;
System.out.println(f);
char c = ' ';
System.out.print(c);
System.out.println("hello");
boolean b = false;
System.out.println(b);| Unit | |
|---|---|
| 1/0 | 1 bit |
| 4 bits | 1 nibble |
| 8 bits | 1 byte |
| 1024 bytes | 1 KB |
| 1024 KB | 1 MB |
| 1024 MB | 1 GB |
| 1024 GB | 1 TB |
1 KB - 1 kilobytes - 1024 bytes - 1024 * 8 bits
1 Kb - 1 kilobits - 1024 bits
| Data Type | Size |
|---|---|
| byte | 1 byte |
| short | 2 byte |
| int | 4 bytes |
| long | 8 bytes |
| float | 4 bytes |
| double | 8 bytes |
| char | 2 bytes |
| String | 2 * no. of chars |
| boolean | 1 bit |
conversion of data from one type to another
Conversion that happens automatically
-
Storing a number to decimal number
-
Storing a small box value into a large box
Conversion done forcefully
- Storing a decimal number into number
- Storing a large box value into small box
left -> right -> Implicit
right->left -> Explicit
long l = 1234747647448l;
float f = l;
System.out.println(f);
double d = 10.3673;
int a = (int)d;
long l = 123436L;
int a = (int) l;
System.out.println(a);
float f = 123.377f;
double d = f;
double d = 13.37484;
float f = (float)d;
System.out.println(f);
int a = 13;
int b = 4;
double d = (double)a / b;
System.out.println(d);
int a = 10;
int b = 0;
int c = a / b;
System.out.println(c);
double d = 192.4894;
int a = (int) d;
System.out.println(a);int- 4 bytes - -2^31 to 2^31-1long- 8 bytes - -2^63 to 2^63-1
Scanner sc = new Scanner(System.in);
nextInt(), nextLong(), nextFloat(), nextDouble(), nextBoolean()
next() - Reads the first word of input
nextLine() - Reads the entire line of input char c = sc.next().charAt(0);
System.out.println(c); System.out.println(Math.max(10, 23));
System.out.println(Math.min(10, 23));
System.out.println(Math.pow(3, 4)); // 3^4
System.out.println(Math.sqrt(25));
System.out.println(Math.round(12.55));
System.out.println(Math.floor(12.99));
System.out.println(Math.ceil(12.23));
System.out.println(Math.ceil(-2.34));
System.out.println(Math.abs(-34));
System.out.println((int)(Math.random() * 10000 + 1000));
int s = 10 * 3 + 4; // 34
int s = 10 / 3 * 2 ; // 6
int s = 10 * 3 / 2 ; // 15
int s = 10 * (3 / 2);
System.out.println(s);If
if(condition) {
// statement/s;
}<, >, <=, >=, == (equals to), != (not equals to)
&&, ||, !
Precedence of logical operators - ! && ||
// Check whether a number is in a range of 1 to 100
int a = sc.nextInt();
if(1 <= a && a <= 100) {
System.out.println("In range");
}
else {
System.out.println("Not in range");
}
- a-z -> 97-122
- A-Z -> 65-90
- 0-9 -> 48-57
char c = sc.next().charAt(0);
if(c >= 'a' && c <= 'z') {
char c2 = (char)(c - 32);
System.out.println(c2);
}- divisible by 4 and not by 100 -> 2012, 2016, 2020, 1996
- divisible by 100 and by 400 -> 1600, 2000, 2400
int a = 5;
if(a > 10) {
System.out.println("Hello");
}
else {
System.out.println("Hello 2");
}
else { // error: else without if
System.out.println("Hello 3");
} if(a > 3)
System.out.println("Hello");
System.out.println("Hello 3");
else // error: else is without
System.out.println("Hello 2"); int a = 5;
if(a < 10)
if(a > 20)
System.out.println("Hello");
else
System.out.println("Hello 2");
int a = 5;
if(a > 10)
if(a > 20)
System.out.println("Hello");
else
System.out.println("Hello 2");
else
System.out.println("Hello 3");
int a = 5;
if(a > 10)
if(a > 20)
System.out.println("Hello");
else if(a < 15)
System.out.println("Hello 2");
else
System.out.println("Hello 3");
Runs a code for some fixed number of times/iterations
- I -> C -> B -> U -> C -> B -> U -> C -> B -> U -> C -> B -> U -> C
// Product of all numbers from 1 to 10
int p = 1;
for(int i = 1; i <= 10; i = i + 1) {
p = p * i;
}
System.out.println(p);- Factorial of a number
int n = sc.nextInt();
int f = 1;
for(int i = 1; i <= n; i = i + 1) {
f = f * i;
}
System.out.println(f);
for(int i = 1; i <= 10; i = i + 1) {
if(i == 5) {
break;
}
System.out.println(i);
}
for(int i = 1; i <= 10; i = i + 1) {
if(i == 5) {
continue;
}
System.out.println(i);
}- While loop
- C -> B -> C -> B -> C
// Print all digits of a number
int n = 3284;
int p = n;
while(n > 0) {
int d = n % 10;
System.out.println(d);
n = n / 10;
}
System.out.println(p);
- Find the reverse of the number
int n = 23178;
while(n > 0) {
int d = n % 10;
System.out.print(d);
n = n / 10;
}- Count trailing zeros in a number
int a = 102300;
int ct = 0;
while(a > 0) {
int d = a % 10;
if(d == 0) {
ct = ct + 1;
}
else {
break;
}
a = a / 10;
}
System.out.println(ct);- Factors of number
int n = 24;
for(int i = 1; i <= n; i = i + 1) {
if(n % i == 0) {
System.out.println(i);
}
}-
B -> C -> B -> C -> B -> C
-
Entry controlled loops -These are loops where condition check is happening prior to the body. Ex:for,while -
Exit controlled loops -These are loops where condition check happens after the body. Ex:do while
- Find the sum of digits of all the numbers in range of 1 to 50
for(int i = 1; i <= 50; i++) {
int n = i;
int sum = 0;
while(n != 0) {
int d = n % 10;
sum = sum + d;
n = n / 10;
}
System.out.println(sum);
}- Find all the prime numbers in the range of 1 to 100
for(int j = 1; j <= 100; j = j + 1) {
int n = j;
int ct = 0;
for(int i = 1; i <= n; i = i + 1) {
if(n % i == 0) {
ct++;
}
}
if(ct == 2) {
System.out.println(n);
}
}
- Outer loop should run for the number of rows in pattern
- Inner loop should run for number of values in each row
for(int i = 1; i <= 5; i = i + 1) {
for(int j = 1; j <= i; j = j + 1) {
System.out.print(j);
}
System.out.println();
}
// 1
// 12
// 123
// 1234
// 12345
Small code that does some small work
-
DRYPrinciple - Don't repeat yourself -
return_type-> Data type of the value the function is returning as result. For no result functions we mark it as void -
function_name-> Any name that follows variable naming rules -
list of arguments-> Values which we are giving to the function -
body of function-> logic of function -
Properties of return
- As soon as we hit a return statement in function the function call ends
- A function having a return type as not void it is compulsory to return a value
- A function cannot return multiple values
-
Function definition - Function name, return type, list of arguments and body
-
Function call - the call to the actual function
-
Function signature - Very first line of function definition which includes name, return type and list of arguments
-
Actual parameters/arguments - parameters passed in the function definition
-
Formal parameters/arguments - parameters passed in the function call
