Detailed introduction to Lambda expressions in java

What is a lambda expression?

A lambda expression is a transitive block of code that can be executed one or more times later.

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For example:

class action implements ActionListener{
	@Override
	public void actionPerformed(ActionEvent e){
		System.out.println("now time is"+new Date());
		Toolkit.getDefaultToolkit().beep();
	}

}
public class Main{
	public static void main(String[] args){
		action a=new action();
		Timer timer=new Timer(2000,a);
		timer.start();
		JOptionPane.showMessageDialog(null, "is quit?");
		//这个窗口用于防止main线程执行完毕直接结束
	}

}

The a object of the action class in this code is actually just a code The segment is passed to the constructor of Timer. Because Java is a language based on object-oriented thinking, there is no function call and no code segment transfer, so the required code must be encapsulated in a class, which is the action class above. With lambda expressions, the code can be made more concise.

The above is represented by lambda as follows:

public class Main{
	public static void main(String[] args){
		Timer timer=new Timer(2000,(ActionEvent e)->{
			System.out.println("now the time is"+new Date());
			Toolkit.getDefaultToolkit().beep();
		});
		timer.start();
		//结束
		
	}

}

Using lambda expressions can make the code very concise. If the type of e can be deduced through the following, then the parameter type can be omitted. If there is only one parameter, you can omit the parentheses, as follows:

e->{
System.out.println(“now the time is”+new Date());
Toolkit.getDefaultToolkit().beep();
}

This lambda expression can be equivalent to:

ActionListener al=e->{
System.out.println(“now the time is”+new Date());
Toolkit.getDefaultToolkit().beep();
}

Then throw al into the Timer constructor.

ActionListener As an interface, it has only one abstract method. This is a condition that must be met as a functional interface. Functional interfaces can be written as lambda expressions.

Then implement a code that sorts String arrays by length for easy understanding:

public class Main{
	public static void main(String[] args){
		String[] con=new String[]{"apple","cat","bannane","foot","do"};
		Arrays.sort(con,(str1,str2)->str1.length()-str2.length());
		//第一种实现  这儿因为直接返回值所以没有加"{"和"}"所以也不用加";" 上下文能推断出这是String类型参数，
		//所以不用加参数类型
		Comparator<String> compare = (str1,str2)->s1.length()-s2.length();
		Arrays.sort(con,compare);//第二种实现,还可以采用写一个类实现Comparator中的compare方法
		//如:
		com com1=new com();
		Arrays.sort(con.com1);//其本质都是传递一段代码
	}
	class com implements Compartor<String>{
		@Override
		public void compare(String str1,String str2){
			return str1.length()-str2.length();
		}
	}

}

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