Function pointers in Java
java 8object oriented programmingprogramming
From Java 8 onwards, the lambda expression is introduced which acts as function pointers.
Lambda expressions are introduced in Java 8 and are touted to be the biggest feature of Java 8. Lambda expression facilitates functional programming and simplifies the development a lot.
语法
A lambda expression is characterized by the following syntax.
parameter -> expression body
Following are the important characteristics of a lambda expression.
- Optional type declaration − No need to declare the type of a parameter. The compiler can inference the same from the value of the parameter.
- Optional parenthesis around parameter − No need to declare a single parameter in parenthesis. For multiple parameters, parentheses are required.
- Optional curly braces − No need to use curly braces in expression body if the body contains a single statement.
- Optional return keyword − The compiler automatically returns the value if the body has a single expression to return the value. Curly braces are required to indicate that expression returns a value.
Lambda Expressions Example
Create the following Java program using any editor of your choice in, say, C:\> JAVA.
Java8Tester.java
public class Java8Tester {
public static void main(String args[]) {
Java8Tester tester = new Java8Tester();
//带有类型声明 MathOperation addition = (int a, int b) -> a + b;
//不带有类型声明 MathOperation subtraction = (a, b) -> a - b;
//带有 return 语句和花括号 MathOperation multiplication =
(int a, int b) -> { return a * b; };
//不带有 return 语句和花括号 MathOperation division =
(int a, int b) -> a / b;
System.out.println("10 + 5 = " + tester.operate(10, 5, 加法));
System.out.println("10 - 5 = " + tester.operate(10, 5, 减法));
System.out.println("10 x 5 = " + tester.operate(10, 5, 乘法));
System.out.println("10 / 5 = " + tester.operate(10, 5, 除法));
//不带括号 GreetingServicegreetService1 = message ->
System.out.println("Hello" + message);
//带括号 GreetingServicegreetService2 = (message) ->;
System.out.println("Hello " + message);
greetService1.sayMessage("Mahesh");
greetService2.sayMessage("Suresh");
}
interface MathOperation {
int operation(int a, int b);
}
interface GreetingService {
void sayMessage(String message);
}
private int operate(int a, int b, MathOperation mathOperation) {
return mathOperation.operation(a, b);
}
}
验证结果
使用 javac 编译器编译类，如下所示 −
C:\JAVA>javac Java8Tester.java
现在运行 Java8Tester，如下所示 −
C:\JAVA>java Java8Tester
它应该产生以下输出 −
10 + 5 = 15 10 - 5 = 5 10 x 5 = 50 10 / 5 = 2 Hello Mahesh Hello Suresh
