Cui 
Let’s learn programming in multi-lang mode. Since all languages are trying to express same things just in different grammars.
Main method
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```Java public void main(String[] args) { System.out.println("Hello, World!"); } ``` -
```Kotlin fun main(args: Array<String>) { println("Hello, World!") } ``` -
```Swift func main() { print("Hello, World!") } ``` -
```Python def method(): print("Hello, Main!") if __name__ == "__main__": method() elif __name__ == "module_name": print("Hello, Module!") ```
Data Types
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```Java // Primitive Integer Types byte byteNumber = 10; // 1 byte/8-bit signed integer, range from -128 to 127 short shortNumber = 10; // 2 bytes/16-bit signed integer, range from -32,768 to 32,767 int integerNumber = 10; // 4 bytes/32-bit signed integer, range from -2^31 to 2^31-1 long longNumber = 1000000000L; // 8 bytes/64-bit signed integer, range from -2^63 to 2^63-1 // Primitive Floating point Types float floatNumber = 10.0f; // 4 bytes/32-bit floating point number, 6-7 decimal digits double doubleNumber = 10.0d; // 8 bytes/64-bit floating point number, 15 decimal digits float scientificNotation = 35e3f; // 35.0 x 10^3 double scientificNotation = 12E4; // 12.0 x 10^4 // Primitive Boolean Types boolean isTrue = true; // 1-bit true/false value // Primitive Character Types char character = 'a'; // 2 bytes/16-bit Unicode character char myLetter = 66; // ASCII value for 'B' // Reference Types - String String string = "Hello, World!"; // Reference Types - Arrays List<String> list = new ArrayList<>(); Set<String> set = new HashSet<>(); Map<String, String> map = new HashMap<>(); Collection<String> collection = Collections.emptyList(); // Reference Types - Classes/Objects CustomObject customObject = new CustomObject(); ``` -
```Kotlin // Number Integer Types val byteNumber: Byte = 10 // 1 byte/8-bit signed integer, range from -128 to 127 val shortNumber: Short = 10 // 2 bytes/16-bit signed integer, range from -32,768 to 32,767 val integerNumber: Int = 10 // 4 bytes/32-bit signed integer, range from -2^31 to 2^31-1 val longNumber: Long = 1_000_000_000L // 8 bytes/64-bit signed integer, range from -2^63 to 2^63-1 // You can miss type declaration and let Kotlin infer the type val myMaxInt = 2_147_483_647 // type inferred as Int val myLong = 2_147_483_648 // type inferred as Long // Number Floating point Types val floatNumber: Float = 10.0f // 4 bytes/32-bit floating point number, 6-7 decimal digits val doubleNumber: Double = 10.0 // 8 bytes/64-bit floating point number, 15 decimal digits val myFloat = 35E3F // 35.0 x 10^3 val myDouble = 12E4 // 12.0 x 10^4 // Boolean Types val isTrue: Boolean = true // 1-bit true/false value // Char Types val character: Char = 'a' // 2 bytes/16-bit Unicode character //val myLetter: Char = 66 // Error: Kotlin doesn't support ASCII values for char // Strings Types val string: String = "Hello, World!" // String length val length = string.length // Accessing characters val firstChar = string[0] // Modifying strings //string[0] = 'h' // Error: Strings are immutable in Kotlin // Arrays Types var intArray = intArrayOf(1, 2, 3, 4, 5) var longArray = longArrayOf(1L, 2L, 3L, 4L, 5L) var floatArray = floatArrayOf(1.1f, 2.2f, 3.3f, 4.4f, 5.5f) var doubleArray = doubleArrayOf(1.1, 2.2, 3.3, 4.4, 5.5) var booleanArray = booleanArrayOf(true, false, true) var charArray = charArrayOf('a', 'b', 'c') var stringArray = arrayOf("Hello", "World") // Array size var size = stringArray.size // Accessing elements var element = stringArray[0] // Modifying elements stringArray[0] = "Hi" // Collections Types val list: List<String> = listOf() var set: Set<String> = mutableSetOf() var map: Map<String, String> = mapOf("key" to "value") ``` -
```Swift pputs 'hello' ``` -
```Python """ Text Type: str Numeric Types: int, float, complex Sequence Types: list, tuple, range Mapping Type: dict Set Types: set, frozenset Boolean Type: bool Binary Types: bytes, bytearray, memoryview None Type: NoneType """ # Explicitly specify the data type x = str("Hello World") # str x = int(20) # int x = float(20.5) # float x = complex(1j) # complex x = list(("apple", "banana", "cherry")) # list x = tuple(("apple", "banana", "cherry")) # tuple x = range(6) # range x = dict(name="John", age=36) # dict x = set(("apple", "banana", "cherry")) # set x = frozenset(("apple", "banana", "cherry")) # frozenset x = bool(5) # bool x = bytes(5) # bytes x = bytearray(5) # bytearray x = memoryview(bytes(5)) # memoryview ```
Operators & Maths
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```Java 1 + 1 # => 2 8 - 1 # => 7 10 * 2 # => 20 36 / 5 # => 7 36.0 / 5.0 # => 7.2 36 % 5 # => 1 i++ # => i+1 ++i # => i+1 i-- # => i-1 --i # => i-1 && # => and || # => or ! # => not ``` -
```Kotlin console.log('hello'); ``` -
```Swift pputs 'hello' ``` -
```Python 1 + 1 # => 2 8 - 1 # => 7 10 * 2 # => 20 36 / 5 # => 7.2 36 // 5 # => 7 36 % 5 # => 1 2 ** 3 # => 2^3 => 8 2 ** 0.5 # => sqrt(2) => 1.4142135623730951 2 ** -1 # => 1/2 => 0.5 True # => True 1 False # => False 0 and # => && or # => || not # => ! (not > and > or) True + True # => 2 True * 8 # => 8 False - 5 # => -5 0 == False # => True 1 == True # => True 2 == True # => False -5 != False # => True bool(0) # => False bool(0.0) # => False bool(1) # => True bool(2) # => True bool(-5) # => True 0 and 2 # => 0 `and` return the second value if both are True, otherwise return the first False value. 0 or 2 # => 2 `or` return the first True value if encountered 0 and 2 or 3 # => 3 `and` return 0, `or` return 3 ```
If-Else
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```Java var_dump('hello'); ``` -
```Kotlin console.log('hello'); ``` -
```Swift pputs 'hello' ``` -
```Python print('hello') ```
Switch
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```Java var_dump('hello'); ``` -
```Kotlin console.log('hello'); ``` -
```Swift pputs 'hello' ``` -
```Python print('hello') ```
For Loop
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```Java var_dump('hello'); ``` -
```Kotlin console.log('hello'); ``` -
```Swift pputs 'hello' ``` -
```Python print('hello') ```
While Loop
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```Java var_dump('hello'); ``` -
```Kotlin console.log('hello'); ``` -
```Swift pputs 'hello' ``` -
```Python print('hello') ```
Functions/Methods
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```Java var_dump('hello'); ``` -
```Kotlin console.log('hello'); ``` -
```Swift pputs 'hello' ``` -
```Python print('hello') ```
Lambda
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```Java var_dump('hello'); ``` -
```Kotlin console.log('hello'); ``` -
```Swift pputs 'hello' ``` -
```Python print('hello') ```
Classes/Objects
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```Java var_dump('hello'); ``` -
```Kotlin console.log('hello'); ``` -
```Swift pputs 'hello' ``` -
```Python print('hello') ```