20가지 자바 모범 사례

코드 품질을 향상시키는 데 도움이 되는 몇 가지 Java 모범 사례입니다.

1- 가능하면 프리미티브 래퍼보다 프리미티브를 선호합니다.

Long idNumber;
long idNumber; // long takes less memory than Long

int birthYear;
short birthYear; // better because birth year can not be more than 32767


int personRunningSpeedKmHour;
byte personRunningSpeedKmHour; // better because a person can not have
// more than 127 km/h as speed

public boolean isOdd(int num) {
return (num & 1) != 0;
} 
// best way to check the oddity of a number

String name = null; // redundant
int speed = 0; // redundant
boolean isOpen = false; // redundant


String name; 
int speed;
boolean isOpen;
// same values in a cleaner way

public int age; // very bad
int age; // bad
private int age; // good

String s1 = new String("AnyString") ; // bad : low instantiation
// The constructor creates a new object, and adds the literal to the heap


String s2 = "AnyString" ; // good: fast instantiation
// This shortcut refers to the item in the String pool 
// and creates a new object only if the literal is not in the String pool.

String address = streetNumber +" "+ streetName +" "
+cityName+" "+cityNumber+" "+ countryName; // bad


StringBuilder address = new StringBuilder(streetNumber).append(" ")
.append(streetName).append(" ").append(cityName).append(" ")
.append(cityNumber).append(" ").append(countryName); // good

8- 숫자 리터럴에서 밑줄 사용.

int myMoneyInBank = 58356823;
int myMoneyInBank = 58_356_823; // more readable

long billsToPay = 1000000000L;
long billsToPay = 1_000_000_000L; // more readable

for (int i = 0; i < names.length; i++) 
{ saveInDb(names[i]); }


for (String name : names) 
{ saveInDb(name); } // cleaner

Scanner scanner = null;
try
{scanner = new Scanner(new File("test.txt"));
while (scanner.hasNext())
{System.out.println(scanner.nextLine());}} 
catch (FileNotFoundException e) 
{e.printStackTrace();} 
finally 
{if (scanner != null) 
{scanner.close();}}
// error-prone as we can forget to close the scanner in the finally block



try (Scanner scanner = new Scanner(new File("test.txt"))) 
{while (scanner.hasNext()) 
{System.out.println(scanner.nextLine());}} 
catch (FileNotFoundException fnfe) 
{fnfe.printStackTrace();} 
// cleaner and more succinct

try
{ productPrice = Integer.parseInt(integer); } 
catch (NumberFormatException ex)
{ } 
// fail silently without giving any feedback


try 
{ productPrice = Integer.parseInt(integer); } 
catch (NumberFormatException ex) 
{unreadablePrices.add(productPrice); // handle error
log.error("Cannot read price : ", productPrice );// proper and meaningful message
}

• Null 요소를 반환하는 대신 빈 컬렉션 반환
• Optional당신이 할 수있는대로 사용
• requireNonNull방법java.utils.Objects
• NotNull, NotEmpty, NotBlank주석
• Objects::nonNull~에Streams
• requireNonNull방법java.util.Objects

14- 동등성을 확인하려면 ==참조 및 equals개체 에 사용하십시오.

// prerequisite:  the person class overrides equals() and hashCode()
Person p1 = new Person("John","Doe");
Person p2 = new Person("John","Doe");

System.out.println(p1 == p2); // false
System.out.println(p1.equals(p2)); // true

15- equals를 구현할 때 항상 hashCode를 구현하십시오.
hashCode재정의 하는 경우 equals"계약 위반"을 방지하기 위해 항상 재정의해야 합니다 .
API에 따라 hashCode()두 개체에 대한 메서드 에서 반환된 결과는 해당 메서드가 동등하다고 표시하는 경우 동일해야 합니다 . equals그 반대가 반드시 참인 것은 아닙니다 .

16-불변 데이터에 대한 선호 레코드(java14부터)

public final class Person {
    private final String name;
    private final long idNumber;

    public Person(String name, long idNumber) {
        this.name = name;
        this.idNumber = idNumber;
    }

    public boolean equals(Object other) {
        if (other == this) return true;
        if (other == null) return false;
        if (other.getClass() != this.getClass()) return false;
        Person that = (Person) other;
        return (this.name.equals(that.name)) && (this.idNumber == that.idNumber);
    }

    public String toString() {
        return name + " " + idNumber;
    }

    public int hashCode() {
        return Objects.hash(idNumber, name);
    }
}



// this class can be transformed to a record:
record Person(String name, long idNumber) { } // cleaner and less verbose

public final class MyValues {
  private MyValues() {
    // No need to instantiate the class, we can hide its constructor
  }
  public static final String VALUE1 = "foo";
  public static final String VALUE2 = "bar";
}

// <-- empty line
@Repository
public class ...

20- java.handling.java.localDateTime자바 8부터 날짜 유형 처리가 권장됩니다.

더 많은 Java 모범 사례를 보려면 Clean code 및 Effective java 라는 훌륭한 책을 추천합니다 .