JavaScript有Array.join()

js>["Bill","Bob","Steve"].join(" and ")
Bill and Bob and Steve

Java有这样的东西吗?我知道我可以用StringBuilder自己拼凑一些东西:

static public String join(List<String> list, String conjunction)
{
   StringBuilder sb = new StringBuilder();
   boolean first = true;
   for (String item : list)
   {
      if (first)
         first = false;
      else
         sb.append(conjunction);
      sb.append(item);
   }
   return sb.toString();
}

. .但是如果像这样的东西已经是JDK的一部分,那么这样做就没有意义了。


当前回答

如果您正在使用Eclipse Collections(以前的GS Collections),则可以使用makeString()方法。

List<String> list = Arrays.asList("Bill", "Bob", "Steve");

String string = ListAdapter.adapt(list).makeString(" and ");

Assert.assertEquals("Bill and Bob and Steve", string);

如果您可以将List转换为Eclipse Collections类型,那么您就可以摆脱适配器。

MutableList<String> list = Lists.mutable.with("Bill", "Bob", "Steve");
String string = list.makeString(" and ");

如果您只想要一个逗号分隔的字符串,您可以使用不接受参数的makeString()版本。

Assert.assertEquals(
    "Bill, Bob, Steve", 
    Lists.mutable.with("Bill", "Bob", "Steve").makeString());

注意:我是Eclipse Collections的提交者。

其他回答

String.join

在Java 8中,你不需要任何第三方库就可以做到这一点。

如果你想加入一个字符串集合,你可以使用String.join()方法:

List<String> list = Arrays.asList("foo", "bar", "baz");
String joined = String.join(" and ", list); // "foo and bar and baz"

Collectors.joining

如果你有一个非String类型的Collection,你可以使用Stream API来连接Collector:

List<Person> list = Arrays.asList(
  new Person("John", "Smith"),
  new Person("Anna", "Martinez"),
  new Person("Paul", "Watson ")
);

String joinedFirstNames = list.stream()
  .map(Person::getFirstName)
  .collect(Collectors.joining(", ")); // "John, Anna, Paul"

StringJoiner类可能也很有用。

你可以从Spring框架的StringUtils中使用它。我知道它已经被提到过,但是实际上您可以只使用这段代码,它就可以立即工作,而不需要Spring。

// from https://github.com/spring-projects/spring-framework/blob/master/spring-core/src/main/java/org/springframework/util/StringUtils.java

/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
public class StringUtils {
    public static String collectionToDelimitedString(Collection<?> coll, String delim, String prefix, String suffix) {
        if(coll == null || coll.isEmpty()) {
            return "";
        }
        StringBuilder sb = new StringBuilder();
        Iterator<?> it = coll.iterator();
        while (it.hasNext()) {
            sb.append(prefix).append(it.next()).append(suffix);
            if (it.hasNext()) {
                sb.append(delim);
            }
        }
        return sb.toString();
    }
}

使用java 8收集器,这可以用以下代码完成:

Arrays.asList("Bill", "Bob", "Steve").stream()
.collect(Collectors.joining(" and "));

此外,java 8中最简单的解决方案:

String.join(" and ", "Bill", "Bob", "Steve");

or

String.join(" and ", Arrays.asList("Bill", "Bob", "Steve"));

用java 1.8的流可以使用,

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

List<String> list = Arrays.asList("Bill","Bob","Steve").
String str = list.stream().collect(Collectors.joining(" and "));

Java 8确实带来了

Collectors.joining(CharSequence delimiter, CharSequence prefix, CharSequence suffix)

方法,通过对空值使用前缀+后缀,该方法为nullsafe。

它可以以以下方式使用:

String s = stringList.stream().collect(Collectors.joining(" and ", "prefix_", "_suffix"))

收藏家。join (CharSequence delimiter)方法只是在内部调用joining(delimiter, "", "")。