Lambda expression
Lambda expression refers to a simplified definition form applied in the context of a single abstract method (SAM) interface, which can be used to solve the complex problem of anonymous inner class definition.
Lambda expression syntax:
(参数)->方法体
Method body equivalent to subclass overriding abstract method
Example: Getting started with Lambda expressions
package Project.Study.Lambda_test;
interface IMessage{
public void print();
}
public class Test1 {
public static void main(String [] args){
//此处为Lambda表达式，没有任何输入参数，只是进行输出操作
fun(()->System.out.println("Hello World"));
}
public static void fun(IMessage msg){
msg.print();
}
}
//结果：
//Hello World
Example: Using anonymous inner classes for the above operations
package Project.Study.Lambda_test;
interface IMessage{
public void print();
}
public class Test1 {
public static void main(String [] args){
fun(new IMessage() { //等价于Lambda表达式定义
@Override
public void print() {
System.out.println("Hello World");
}
});
}
public static void fun(IMessage msg){
msg.print();
}
}
//结果：
//Hello World
In order to distinguish the interface used by the Lambda expression, you can use the "@FunctionalInterface" annotation on the interface to declare that this is a functional interface. Only one abstract method is allowed to be defined.
Example: Functional interface
@FunctionalInterface
interface IMessage{
public void print();
}
Example: Define a method with parameters and return values
package Project.Study.Lambda_test;
interface IMessage{
public int add(int x,int y);
}
public class Test1 {
public static void main(String [] args){
fun((s1,s2)->{
return s1-s2;
});
}
public static void fun(IMessage msg){
System.out.println(msg.add(10,20));
}
}
//结果：
//-10
Example: Passing variable parameters
package Project.Study.Lambda_test;
@FunctionalInterface
interface IMessage2{
public int add(int...args);
static int sum(int...args){ //此方法可以由接口名称直接调用
int sum=0;
for(int temp:args){
sum+=temp;
}
return sum;
}
}
public class Test2 {
public static void main(String [] args){
//在Lambda表达式中则直接调用接口里定义的静态方法
fun2((int...param)->IMessage2.sum(param));
}
public static void fun2(IMessage2 msg){
System.out.println(msg.add(10,20,30)); //传递可变参数
}
}
