What is the difference between Java functions and Kotlin language functions?

The difference between Java and Kotlin functions: Syntax: Java functions need to specify parameter types and names, while Kotlin can omit the type and use lambda expressions; Parameters: Kotlin can omit parameter types using a more concise syntax; Return value: Kotlin can Omit the return value type, which defaults to Unit; extension function: Kotlin can add new functions to existing classes, while Java needs to implement similar functions through inheritance; instance method call: Kotlin can omit the object name and use a more concise syntax.

The difference between Java functions and Kotlin language functions

Syntax:

• Java function: public static void main(String[] args)
• Kotlin function: fun main(args: Array<string>)</string>

Parameters:

• Java function: parameter type and name need to be specified explicitly
• Kotlin function: parameter type can be omitted, parameter name is optional

Return value:

• Java function: the return value type must be specified
• Kotlin function: the return value type can be omitted ( Default is Unit)

Lambda expression:

• Java: Need to implement the interface and override the method
• Kotlin: Use {} directly to define lambda expressions

Example:

// Java 函数
public static void main(String[] args) {
    System.out.println("Hello Java!");
}

// Kotlin 函数
fun main(args: Array<String>) {
    println("Hello Kotlin!")
}

Extension function:

• Kotlin’s unique feature, you can add new functions to existing classes
• Java needs to inherit or use proxy classes to achieve similar functions

Instance method call:

• Java: via object name.Method name
• Kotlin: via object.Method name (optional)

Practical case:

Consider a function that calculates the sum of two numbers:

// Java 函数
public static int add(int a, int b) {
    return a + b;
}

// Kotlin 函数
fun add(a: Int, b: Int) = a + b

In Java, you need to specify parameter types and names explicitly. But in Kotlin, you can omit parameter types and use a cleaner syntax. In addition, in Kotlin, you can add a plus function to the Int class through an extension function to make the code more readable:

fun Int.plus(other: Int) = this + other

In this way, you The sum of numbers can be calculated like this:

val sum = 10.plus(20)

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