[未优雅地处理尾随和前导的null/空值。现在已经更好地工作了。]
我的看法是,使用Google Guava(不是官方的Java包,但非常好用)。我提供这个方法是因为你似乎考虑过使用Joiner,但最终拒绝了它。所以既然你曾经愿意使用Joiner,也许现在你想再次考虑它:
package testCode;
import java.util.List;
import com.google.common.base.Joiner;
import com.google.common.base.Predicate;
import com.google.common.base.Strings;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
public class TestClass {
Joiner joinComma = Joiner.on(", ");
Joiner joinAndForTwo = Joiner.on(" and ");
Joiner joinAndForMoreThanTwo = Joiner.on(", and ");
public String joinWithAnd(List<String> elements) {
ImmutableList<String> elementsNoNullsOrEmpties = new ImmutableList.Builder<String>()
.addAll(Iterables.filter(elements, new Predicate<String>() {
@Override
public boolean apply(String arg0) {
return !Strings.isNullOrEmpty(arg0);
}
})).build();
if (elementsNoNullsOrEmpties.size() == 0) {
return null;
} else if (elementsNoNullsOrEmpties.size() == 1) {
return Iterables.getOnlyElement(elementsNoNullsOrEmpties);
} else if (elementsNoNullsOrEmpties.size() == 2) {
return joinAndForTwo.join(elementsNoNullsOrEmpties);
} else {
final List<String> leadingElements = elementsNoNullsOrEmpties
.subList(0, elementsNoNullsOrEmpties.size() - 1);
final String trailingElement = elementsNoNullsOrEmpties
.get(elementsNoNullsOrEmpties.size() - 1);
return joinAndForMoreThanTwo.join(joinComma.join(leadingElements),
trailingElement);
}
}
}
还有测试驱动程序:
package testCode;
import java.util.List;
import com.google.common.collect.Lists;
public class TestMain {
static List<String> test1 = Lists.newArrayList();
static List<String> test2 = Lists.newArrayList("");
static List<String> test3 = Lists.newArrayList("a");
static List<String> test4 = Lists.newArrayList("a", "b");
static List<String> test5 = Lists.newArrayList("a", "b", "c", "d");
static List<String> test6 = Lists.newArrayList("a", "b", "c", null, "d");
static List<String> test7 = Lists.newArrayList("a", "b", "c", null);
static List<String> test8 = Lists.newArrayList("a", "b", "", "", null, "c",
null);
static List<String> test9 = Lists.newArrayList("", "a", "b", "c", null);
static List<String> test10 = Lists.newArrayList(null, "a", "b", "c", null);
public static void main(String[] args) {
TestClass testClass = new TestClass();
System.out.println(testClass.joinWithAnd(test1));
System.out.println(testClass.joinWithAnd(test2));
System.out.println(testClass.joinWithAnd(test3));
System.out.println(testClass.joinWithAnd(test4));
System.out.println(testClass.joinWithAnd(test5));
System.out.println(testClass.joinWithAnd(test6));
System.out.println(testClass.joinWithAnd(test7));
System.out.println(testClass.joinWithAnd(test8));
System.out.println(testClass.joinWithAnd(test9));
System.out.println(testClass.joinWithAnd(test10));
}
}
输出结果:
null
null
a
a 和 b
a、b、c 和 d
a、b、c 和 d
a、b 和 c
a、b 和 c
a、b 和 c
a、b 和 c
我喜欢这个方法,因为它不使用任何字符串拼接。它将提供的字符串列表分区,然后根据元素数量使用规则正确地将它们粘合在一起,而不是事后再添加"and"。我还处理了所有可能出现的空值/空元素的边界情况。如果您可以保证不会出现这种情况,那么可以简化此解决方案。
[我的方法与您的略有不同,在只有两个元素时,我不在第一个元素后和 "and"之间加逗号,而在三个或更多元素时,在 "and"之前加逗号。这是一种风格问题。您可以根据逗号的工作方式调整到您喜欢的任何方式。]