[英]How to concat 2 string without + concat() and StringBuffer in java
[英]How to simplify String concat in java?
鑒於以下代碼:
private static final String DELIMITER = " ";
@AfterMapping
protected void createCompactInfo(@MappingTarget User user) {
String vorname = Optional.ofNullable(user.getVorname()).orElse(Strings.EMPTY);
String nachname = Optional.ofNullable(user.getNachname()).orElse(Strings.EMPTY);
String email = Optional.ofNullable(user.getEmail()).orElse(Strings.EMPTY);
String compactInfo =
(vorname
+ DELIMITER
+ nachname
+ DELIMITER
+ (email.isEmpty() ? Strings.EMPTY : "(" + email + ")"))
.trim();
if (compactInfo.isEmpty()) {
user.setCompakt(
Optional.ofNullable(user.getId()).orElse(Strings.EMPTY));
} else {
user.setCompakt(compactInfo);
}
我正在團隊中嘗試和討論最簡單的代碼如何看起來,同時還可以使用以下結構:
一個可能的測試可能是這樣的(這里也可以看到預期的結果):
private static Stream<Arguments> arguments() {
return Stream.of(
Arguments.of("Peter", "Silie", "peter@silie.org", "BOND", "Peter Silie (peter@silie.org)"),
Arguments.of(null, "Silie", "peter@silie.org", "BOND", "Silie (peter@silie.org)"),
Arguments.of("Peter", null, "peter@silie.org", "BOND", "Peter (peter@silie.org)"),
Arguments.of("Peter", "Silie", null, "BOND", "Peter Silie"),
Arguments.of(null, "Silie", null, "BOND", "Silie"),
Arguments.of(null, null, "peter@silie.org", "BOND", "(peter@silie.org)"),
Arguments.of("Peter", null, null, "BOND", "Peter"),
Arguments.of(null, null, null, "BOND", "BOND"));
}
@ParameterizedTest(
name = "{index}" + ". Test: vorname={0}, nachname={1}, email={2}; expected: {3}")
@MethodSource(value = "arguments")
void verifyUserKompakt(
String vorname, String nachname, String email, String kuerzel, String expectedResult) {
// arrange
Base base =
Base.builder()
.vorname(vorname)
.nachname(nachname)
.email(email)
.kuerzel(kuerzel)
.build();
// act
User userResult =
userMapperImpl.doIt(base);
// assert
assertThat(userResult.getUserKompakt()).isEqualTo(expectedResult);
}
歡迎任何想法......我可以嘗試什么?
順便說一句:Java 17 是允許的 :-)
以下代碼似乎非常接近,但如果存在,則不處理電子郵件的大括號:
String compactInfo =
(Stream.of(
user.getVorname(),
user.getNachname(),
user.getEmail())
.map(s -> s != null ? s : "")
.collect(Collectors.joining(" ")))
.trim();
user.setUserKompakt(
compactInfo.isEmpty()
? Optional.ofNullable(user.getKuerzel()).orElse("")
: compactInfo);
由於您已經復制了轉換vorname
、 nachname
和userId
代碼,您可能希望將邏輯提取到Function或UnaryOperator 中,因為它是字符串到字符串的轉換,並且是電子郵件的附加轉換。 例子
import java.util.function.UnaryOperator;
....
private static final String EMPTY = "";
private static final String DELIMITER = " ";
UnaryOperator<String> nameOp = o -> Optional.ofNullable(o).orElse(EMPTY);
UnaryOperator<String> mailOp = o -> Optional.ofNullable(o).map(s -> String.format("(%s)", s)).orElse(EMPTY);
@AfterMapping
protected void createCompactInfo(@MappingTarget User user) {
String compactInfo = Stream.of(nameOp.apply(user.getVorname()),
nameOp.apply(user.getNachname()),
mailOp.apply(user.getEmail()))
.filter(Predicate.not(String::isEmpty))
.collect(Collectors.joining(DELIMITER));
user.setCompakt(compactInfo.isEmpty() ? nameOp.apply(user.getId()) : compactInfo);
}
Java 普通串聯和 StringBuilder/StringBuffer 之間存在巨大的性能差異。
在進行字符串連接時觀察您的方法 createCompactInfo:compactInfo = ... 將導致性能不佳。
我建議您嘗試 StringBuilder 或 StringBuffer。
String 是一個不可變對象,這意味着它的值不能改變,所以每次連接 strA + strB 都會產生一個新對象。
比較普通串聯與 StringBuilder 的性能結果:
public class ConcatenateString {
public static void main (String[] args){
String strFinal = "";
long tStart = System.currentTimeMillis();
for(int i = 0; i < 100000; i ++){
strFinal += "a";
}
long tEnd = System.currentTimeMillis();
long tResult = tEnd - tStart;
System.out.println("Runtime with operator + = "+tResult+" ms");
StringBuilder strBuilder = new StringBuilder();
tStart = System.currentTimeMillis();
for(int i = 0; i < 100000; i ++){
strBuilder.append("a");
}
tEnd = System.currentTimeMillis();
tResult = tEnd - tStart;
System.out.println("Runtime with StringBuilder= "+tResult+" ms");
}
}
結果(位於:Darwin Macs-iMac Darwin Kernel Version 20.6.0:Mon Aug 30 06:12:21 PDT 2021;RELEASE_X86_64 x86_64 - Intel I5 處理器 2.5ghz):
Runtime with operator + = 1469 ms
Runtime with StringBuilder= 2 ms
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