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Lamda expression

Basic concepts

1、 Avoid too many anonymous inner class definitions
2、 You can make your code look simple
3、 Removed a bunch of meaningless code , Leave the core logic
4、 Its essence belongs to the concept of functional programming

The common syntax is as follows ：

(params)-> expression[ expression ]
(params) -> statement[ sentence ]
(params) -> {statements}

Case study ：

new Thread(()-> System.out.println(Thread.currentThread().getName()),"Lamda Threads ").start();

application

Basic use

Functional interface ：

stay jdk8 The functional interface is introduced in , An interface that has only one method is a functional interface .

such as ：

@FunctionalInterface
public interface Runnable {
    
    public abstract void run();
}

public interface St{
    
    public void testMethod();
}

• For functional interfaces , We can go through lamda Expression to create the object of the interface

Case study

/** * @author  A programmer in a wig  */
public class LamdaTest2 {
    
    public static void main(String[] args) {
    
        St st = null;
        // Using anonymous inner classes to implement interfaces 
        st = new St() {
    
            @Override
            public void testMethod() {
    
                System.out.println("st- Anonymous inner class ");
            }
        };
        st.testMethod();
        //Lamda Simplified operation 
        st = ()->{
    
            System.out.println("Lamda Simplified operation ");
        };
        st.testMethod();
    }
}
interface St{
    
    public void testMethod();
}

In the case above ,st = ()->{…}

among () Represents the parameter list of methods in the interface .

{} Write the execution statement of the method in

therefore Lamda The way to simplify the operation is , Implementation interface St, And implementation methods testMethod, Method .

Of course, if there is only one execution statement in the method , We can also simplify ： Omit {}

        //lamda  Simplified operation   There is only one execution statement 
        st = ()->System.out.println(" There is only one sentence to execute Lamda simplify ");
        st.testMethod();

Method implementation with parameters

In the example above , Methods in our interface have no parameters , So we can just write as follows ：

()->{
    statement;}  

If there are parameters , You need to specify the parameters ：

/** * @author  A programmer in a wig  */
public class LamdaTest2 {
    
    public static void main(String[] args) {
    
        St st = null;
        //Lamda Simplified operation , stay （） Specify the parameter type and name in 
        st = (int x)->{
    
            System.out.println("Lamda Simplified operation :"+x);
        };
        st.testMethod(100);
        //lamda  Simplified operation , It can also be in （） Write parameter name only 
        st = (x)->System.out.println(" There is only one sentence to execute Lamda simplify :"+x);
        st.testMethod(1000);
        // In the case of multiple parameters 
        Dk dk = null;
        dk = (String a,int b)-> System.out.println(a+":"+b);
        dk.dkMethod(" Zhang San ",15);

        dk = (a,b)-> System.out.println(a+":"+b);
        dk.dkMethod(" Li Si ",20);
    }
}
interface St{
    
    public void testMethod(int x);
}

interface Dk{
    
    public void dkMethod(String a,int b);
}

Lamda Expression traversal set

Lamda Expressions can simplify Cllection and Map The traversal . Serve directly ：

/** * @author  A programmer in a wig  */
public class LamdaTest3 {
    
    public static void main(String[] args) {
    
        // Get ready List
        List<String> sts = new ArrayList<>();
        sts.add(" Kakasi ");sts.add(" Sasuke ");sts.add(" Naruto ");
        // Use Lamda Traverse , If only one sentence has the following form 
        sts.forEach((s)-> System.out.println(s+":Lamda"));
        System.out.println("-----------------");
        // Use Lamda Traverse , If there are multiple statement operations 
        sts.forEach((s)->{
    
            if(s.length()<3)
                System.out.println(s+":Lamda-2");
        });
        System.out.println("--------map----------");
        // Get ready Map
        Map<Integer,String> map = new HashMap<>();
        map.put(1," Kakasi ");map.put(2," Sasuke ");map.put(3," Naruto ");
        // Use Lamda Traverse , If only one sentence has the following form 
        map.forEach((k,v)-> System.out.println(k+":"+v+" Lamda"));
        System.out.println("-----------------");
        // Use Lamda Traverse , If there are multiple statement operations 
        map.forEach((k,v)-> {
    
            if(v.length()<3)
                System.out.println(k+":"+v+" Lamda-2");
        });
    }
}