Shulou(Shulou.com)06/02 Report--

Chapter 1. The origin of the story

The kindergarten teacher writes a formula "1 + 1 =" on the blackboard, and Xiaoming will fill in the blanks.

Since he has learned the addition of less than 10, Xiao Ming can calculate the problem entirely on his own. the code to simulate the process is as follows:

1 public class Student 2 {3 private String name = null; 4 5 public Student (String name) 6 {7 / / TODO Auto-generated constructor stub 8 this.name = name; 9} 10 11 public void setName (String name) 12 {13 this.name = name;14} 15 16 private int calcADD (int a, int b) 17 {18 return a + b 19} 20 21 public void fillBlank (int a, int b) 22 {23 int result = calcADD (a, b); 24 System.out.println (name + "mental arithmetic:" + a + "+ b +" = "+ result); 25} 26}

When filling in the blanks (fillBalnk), Xiao Ming did some direct mental arithmetic (clacADD) and got the result of 2, and wrote the result in the space. The test code is as follows:

1 public class Test 2 {3 public static void main (String [] args) 4 {5 int a = 1; 6 int b = 1; 7 Student s = new Student ("Xiaoming"); 8 s.fillBlank (a, b); 9} 10}

The running results are as follows:

Xiaoming mental arithmetic: 1 + 1 = 2

This process is done entirely by the instance object of the Student class alone and does not involve a callback mechanism.

Chapter 2. Finding fault with kindergarten teachers

At recess, the kindergarten teacher wrote "168 + 291 =" on the blackboard for Xiaoming to finish, and then went back to the office.

Flower wipe! Why do all the teachers have a problem with Xiaoming? It's obviously super class, okay? At this time, Xiao Ming obviously can no longer rely on mental calculation as above, when Xiao Hong in the class handed over a calculator that can only calculate addition (unscrupulous businessmen)! Xiao Ming happened to know how to use the calculator, so he got the result through the calculator and filled in the blanks.

The code for the calculator is:

1 public class Calculator2 {3 public int add (int a, int b) 4 {5 return a + b politics 6} 7}

Modify the Student class to add methods that use calculators:

1 public class Student 2 {3 private String name = null; 4 5 public Student (String name) 6 {7 / / TODO Auto-generated constructor stub 8 this.name = name; 9} 10 11 public void setName (String name) 12 {13 this.name = name;14} 15 16 @ SuppressWarnings ("unused") 17 private int calcADD (int a, int b) 18 {19 return a + b 20} 21 22 private int useCalculator (int a, int b) 23 {24 return new Calculator (). Add (a, b); 25} 26 27 public void fillBlank (int a, int b) 28 {29 int result = useCalculator (a, b); 30 System.out.println (name + "use calculator:" + a + "+ b +" = "+ result); 31} 32}

The test code is as follows:

1 public class Test 2 {3 public static void main (String [] args) 4 {5 int a = 168; 6 int b = 291; 7 Student s = new Student ("Xiaoming"); 8 s.fillBlank (a, b); 9} 10}

The running results are as follows:

Xiaoming uses calculator: 168 + 291 = 459

The callback mechanism is still not involved in this process, but part of Xiaoming's work has been transferred, which is assisted by calculators.

3. The kindergarten teacher is back.

Found that Xiaoming completed the three-digit addition, the teacher thought Xiaoming is very smart, is a malleable talent. So he wrote "26549 + 16487 =" on the blackboard and asked Xiaoming to fill in the blanks before class, and then went back to the office.

Xiaoming looked at the little friend who was happy outside the classroom and couldn't help feeling sad. If you don't go out to play, this recess will be useless! Looking at the calculator that Xiao Hong handed over again, Xiao Ming came up with a plan: let Xiao Hong do it for you.

Xiao Ming told Xiao Hong that the title was "26549 + 16487 =", then pointed out the exact location of the result, and then went out to play happily.

Here, instead of realizing Xiao Hong alone, we regard this calculator that can only be added and Xiao Hong as a whole, a supercalculator that can calculate the results and fill in the blanks. The parameters that this supercalculator needs to pass are two additions and the position to fill in the blanks, and these contents need to be informed in advance by Xiao Ming, that is, Xiao Ming wants to expose part of his method to Xiao Hong. The easiest way is to tell Xiao Hong his reference and two additions.

Therefore, the add method of the supercalculator should contain two operands and a reference to Xiao Ming himself, as follows:

1 public class SuperCalculator2 {3 public void add (int a, int b, Student xiaoming) 4 {5 int result = a + b 6 xiaoming.fillBlank (a, b, result); 7} 8}

Xiao Ming no longer needs mental arithmetic or a calculator, so there is only one way to ask Xiao Hong for help. The code is as follows:

1 public class Student 2 {3 private String name = null; 4 5 public Student (String name) 6 {7 / / TODO Auto-generated constructor stub 8 this.name = name; 9} 10 11 public void setName (String name) 12 {13 this.name = name;14} 15 16 public void callHelp (int a, int b) 17 {18 new SuperCalculator (). Add (a, b, this) 19} 20 21 public void fillBlank (int a, int b, int result) 22 {23 System.out.println (name + "help Xiaohong calculation:" + a + "+" + b + "=" + result); 24} 25}

The test code is as follows:

1 public class Test 2 {3 public static void main (String [] args) 4 {5 int a = 26549; 6 int b = 16487; 7 Student s = new Student ("Xiaoming"); 8 s.callHelp (a, b); 9} 10}

The running result is:

Xiao Ming asks Xiao Hong to calculate: 26549 + 16487 = 43036

The execution process is as follows: Xiao Ming calls the add method of Xiao Hong (new SuperCalculator ()) through his own callHelp method, and passes in his own reference (this) as a parameter when calling. After using the calculator to get the result, Xiao Hong calls back Xiao Ming's fillBlank method and fills the result in the space on the blackboard.

Lights! lights! At this point, the callback function is officially on the stage, and Xiao Ming's fillBlank method is what we often call a callback function.

In this way, it is obvious that Xiao Ming no longer has to wait until the addition is done and the result is filled on the blackboard to have fun with his friends. Xiao Hong, a supercalculator, does the job of filling in the blanks. The advantages of callbacks are already beginning to show.

Chapter 4. The mother-in-law at the door

There is a gray-haired old woman at the door of the kindergarten. Every day, rain or shine, she stalls there to sell some junk food that is about to expire. Because of his old age, he is a little confused and often doesn't know how much money he has earned. One day, she overheard Xiaoming bragging with his friends about how to fight wits with the help of Xiao Hong. So my mother-in-law decided to find a little red card supercalculator to be her little helper and provide a packet of Weilong spicy gluten as a reward. Xiao Hong could not resist the temptation and agreed.

Looking back at the code in the previous chapter, we found that the add method of the Little Red Card supercalculator requires two integer variables and a Student object, but the old woman is not a student, she is a small vendor, ah, it must be modified here. In this case, we naturally think of inheritance and polymorphism. If we let Xiaoming, a student, and an old woman, a peddler, inherit from a parent class, then we only need to pass a reference to the parent class to the little red card supercalculator.

However, in practical use, considering the single inheritance of java and not wanting to expose too much of its own things to others, it is done here by inheriting from the interface with the inner class.

In other words, Xiao Hong hopes to continue to provide computing services to the children in the class in the future, and at the same time provide accounting services to the old woman, and even expand other people's business in the future, so she has agreed on a method to all her customers. for unified processing, that is, the operands you need and what to do after you have done the calculation. For this unified method, Xiao Hong made an interface and provided it to everyone. The code is as follows:

1 public interface doJob2 {3 public void fillBlank (int a, int b, int result); 4}

Because the inspiration comes from helping Xiaoming fill in the blanks, Xiao Hong retains her original intention and does all her business as fillBlank.

At the same time, Xiao Hong modifies her calculator so that it can handle different people who implement the doJob interface at the same time, as follows:

1 public class SuperCalculator2 {3 public void add (int a, int b, doJob customer) 4 {5 int result = a + b 6 customer.fillBlank (a, b, result); 7} 8}

After Xiao Ming and the old woman get this interface, as long as they implement this interface, it is equivalent to telling Xiao Hong what to do after they get the result according to the unified mode, and use the inner class as mentioned earlier. The code is as follows:

Xiaoming's:

1 public class Student 2 {3 private String name = null; 4 5 public Student (String name) 6 {7 / / TODO Auto-generated constructor stub 8 this.name = name; 9} 10 11 public void setName (String name) 12 {13 this.name = name 14} 15 16 public class doHomeWork implements doJob17 {18 19 @ Override20 public void fillBlank (int a, int b, int result) 21 {22 / / TODO Auto-generated method stub23 System.out.println (name + "help Xiaohong calculation:" + a + "+ b +" = "+ result) 24} 25 26} 27 28 public void callHelp (int a, int b) 29 {30 new SuperCalculator () .add (a, b, new doHomeWork ()); 31} 32}

The old woman's:

1 public class Seller 2 {3 private String name = null; 4 5 public Seller (String name) 6 {7 / / TODO Auto-generated constructor stub 8 this.name = name; 9} 10 11 public void setName (String name) 12 {13 this.name = name 14} 15 16 public class doHomeWork implements doJob17 {18 19 @ Override20 public void fillBlank (int a, int b, int result) 21 {22 / / TODO Auto-generated method stub23 System.out.println (name + "help Xiaohong to get even:" + a + "+" + b + "=" + result + "Yuan") 24} 25 26} 27 28 public void callHelp (int a, int b) 29 {30 new SuperCalculator () .add (a, b, new doHomeWork ()); 31} 32}

The test procedure is as follows:

1 public class Test 2 {3 public static void main (String [] args) 4 {5 int a = 56; 6 int b = 31; 7 int c = 26497; 8 int d = 11256; 9 Student S1 = new Student ("Xiaoming"); 10 Seller S2 = new Seller ("granny"); 11 12 s1.callHelp (a, b); 13 s2.callHelp (c, d) 14} 15}

The running results are as follows:

Xiao Ming asked Xiao Hong to calculate: 56 + 31 = 87 the old woman asked Xiao Hong to get even: 26497 + 11256 = 37753 yuan

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