I think rigor is essential to every programmer, and writing elegant and efficient code is a lifelong pursuit.

preface

I always review the code developed by several members of my team before submitting it. In the past, I passed a lot of unsatisfied code fragments, either written by interns or colleagues with years of development experience. Today, I have a sudden impulse to share some code snippets with you, hoping to bring you some inspiration and inspiration.

The theme

Due to the influence of our stereotypical thinking, we write code, in many cases without others to remind us, it is difficult to find something wrong.

Poor command of MAP

Student Student =new Student(" 新 Student "); Map<String, Object> map3 = new HashMap<String, Object>(); Map3. put("k", "k"); map3.put("v", student.getCollogeName()); resultlist.add( map3); Map<String, Object> map4 = new HashMap<String, Object>(); Map4. put("k", "professional "); map4.put("v", student.getMajorName()); resultlist.add( map4); Map<String, Object> map5 = new HashMap<String, Object>(); Map5. put("k", "class "); map5.put("v", student.getBjmc()); resultlist.add(map5);Copy the code

As you can see from the above code, this developer probably started with a single map and found that all maps after list.add were the last one. The initial code looks like this

Student Student =new Student(" 新 Student "); Map<String, Object> map = new HashMap<String, Object>(); Map. Put ("k", "college "); map.put("v", student.getCollogeName()); resultlist.add( map3); Map. Put ("k", "professional "); map.put("v", student.getMajorName()); resultlist.add( map);Copy the code

Such code causes the map to be overwritten because the key is the same. So what’s wrong with changing to his code? Mainly is the problem that the variable name, according to this logic, for example, the next time you need map6, map7, map8, this variable to maintain a few times, delete, increase is elegant, might as well to:

Student Student =new Student(" 新 Student "); Map<String, Object> map = new HashMap<String, Object>(); Map. Put ("k", "college "); map.put("v", student.getCollogeName()); resultlist.add( map3); map = new HashMap<String, Object>(); Map. Put ("k", "professional "); map.put("v", student.getMajorName()); resultlist.add( map);Copy the code

This way, every time you create a new HashMap, you can eliminate the problem of having an inelegant name. Add k and v keys to map.

Student Student =new Student(" 新 Student "); Resultlist. add(new MapKV(" college ", student.getcollogename ())); Resultlist. add(new MapKV(" professional ", student.getmajorName ()));Copy the code

And this MapKV, I don’t need to tell you anything, just has two strings, k and v.

I am not sure about mybatis

public interface QuestionDao {
    List<Question> getQuestionList();
}
Copy the code

Corresponding map file questionmapper.xml

List<Question> questionList = QuestionDao.findBy(params); If (mexamList == null) {// Throw exception}Copy the code

The dao layer of Mybatis cannot return a null list, even if size()=0 only returns a new list, so there is no need to determine the list is null

The equals are not ripe

If (user.get("sl").equals(" sl")) {Copy the code

Many people say that this error is impossible, if the front is null, it will report an error, but I have searched the previous project globally, it is inevitable to find one or two, after all, there are historical legacy problems, intern problems and so on. Because we know null can’t change.equals to:

If (" equals ".equals(user.get("sl"))) {Copy the code

The abuse of the toString

user.get("sl").toString();Copy the code

An error is reported if the preceding value is null. Null cannot have any methods.

On the return are not ripe

Public String getResult() {if (" condition ") {// return "result "; }else {// a bunch of code return "result "; }}Copy the code

Now that there is a return to make sure that the following code does not go, you can rest assured that the bold release

Public String getResult() {if (" condition ") {// return "result "; } // a bunch of code return "result "; }Copy the code

Will not use continue, break, if too long

For example, when searching for a name in a list, break the name in time to save CPU.

for (int i = list.size() - 1; i >= 0; I -) {if (" Shao Lei ". The equals (list) get (I)) getName ())) {user = list. Get (I); }}Copy the code

Instead of

for (int i = list.size() - 1; i >= 0; I -) {if (" Shao Lei ". The equals (list) get (I)) getName ())) {user = list. Get (I); break; }}Copy the code

Suppose that no operation is performed except for a named person, the code looks like this:

for (int i = list.size() - 1; i >= 0; I -) {if (" Shao Lei ". The equals (list) get (I)) getName ())) {/ / there are only two things. user=list.get(i); }else{// do a lot of things here}}Copy the code

In this case, we can drop the if and use the continue

for (int i = list.size() - 1; i >= 0; I -) {if (" Shao Lei ". The equals (list) get (I)) getName ())) {/ / there are only two things. user=list.get(i); continue; } // Do a lot of things here}Copy the code

Continue: exits the current loop and continues with the next loop break: exits the body of the function and continues with the body of the function outside the loop return: exits the entire body of the function and the rest of the body is not executed

Not familiar with the for loop

if (list.size()==0) { for (int i = list.size() - 1; i >= 0; I --) {// do something}}Copy the code

And we know that even list.size()==0 doesn’t affect the code, so let’s just do it

for (int i = list.size() - 1; i >= 0; I --) {// do something}Copy the code

Wrong with try catch

Try catch wrap a chunk

} catch (Exception e) {// error}Copy the code

As to

Try {// this code may be abnormal} catch (Exception e) {// this code is not abnormal // this code is not abnormalCopy the code

This is more readable and elegant, and of course throws can also be used to catch exceptions. Try catch is in the for loop

for (int i = list.size() - 1; i >= 0; I --) {try {catch (Exception e) {catch (Exception e) {Copy the code

We know that a trycatch is going to wrap the whole code around it, and it’s going to be an expensive, frequent trycatch, and except for special cases, you can extract the method and wrap it around it.

Duplicate code snippets

For example, if a method is called multiple times in a class, and only some variables are different, you can extract methods and variables to make the code concise

Don’t use case

If (type = = 1) {} else if (type = = 2) {} else if (type = = 3) {} else if (type = = 4) {}.....................Copy the code

This would be a very long if, and we know that string matching can also be solved using case. In Java 7 and above, case strings are supported.

Switch (argument) {case constant expression 1: break; Case constant expression 2: break; . default: break; }Copy the code

Lazy loading is not used

Such as

String STR = "STR "; if (i == 1){ list.add(str); }Copy the code

Can be changed to

If (I == 1){String STR = "STR "; list.add(str); }Copy the code

Keep creating object references

for (int i = 1; i <= 100; i++) { Object obj = new Object(); // Other code}Copy the code

This will only open up many Object references in memory

Object obj; for (int i = 1; i <= 100; i++) { obj = new Object(); // Other code}Copy the code

conclusion

We solve the problem, may have many kinds of ideas, but also can write many kinds of code, but the code to write elegant is a skill, of course, the first part of the introduction, attention is high, I continue to update. Finally, I’d like to add that I’m not actually a Virgo, but that’s what people call me, so I’ll take it.

If you feel good, remember to pay attention to me! The Denver nuggets: juejin. Cn/user / 272334…