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嗨，我对您如何比较三件事感到非常迷茫。教科书的例子是：

Scanner input = new Scanner(System.in);

System.out.print("Enter the first city: ");
String city1 = input.nextLine();
System.out.print("Enter the second city: ");
String city2 = input.nextLine();
System.out.print("Enter the third city: ");
String city3 = input.nextLine();

if (city1.compareTo(city2) < 0)
  System.out.println("The cities in alphabetical order are:");
  System.out.println(city1);
  System.out.println(city2);

else
  System.out.println("The cities in alphabetical order are:");
  System.out.println(city2);
  System.out.println(city1);

那么你将如何比较第三个并按字母顺序排列？

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1 回答 1

0

您可以使用内置的排序算法（或您自己的）按字母顺序排序，术语是字典顺序的。例如通过使用Collections#sort（文档）。请注意，Strings 是可比较的，默认情况下使用字典顺序。这就是您不需要显式指定顺序的原因，例如通过使用Comparator对象。

此代码段对城市进行排序并打印它们：

List<String> cities = Arrays.asList({city1, city2, city3});
Collections.sort(cities);

System.out.println("Cities sorted lexicographical:");
for (String city : cities) {
    System.out.println(city);
}

或者，如果您更喜欢使用紧凑的Java 8解决方案Streams（它基本上回退到相同的方法，尤其是相同的排序方法）：

Stream.of(city1, city2, city3).sorted().forEach(System.out::println);

请注意，该String#compareTo方法还比较字典顺序，如前所述。因此，您也可以直接对比较进行硬编码（就像您已经尝试过的那样），而不是使用排序算法（compareTo以一种聪明的方式检查结果）：

String smallestCity;
if (city1.compareTo(city2) < 0 && city1.compareTo(city3) < 0) {
    smallestCity = city1;
} else if (city2.compareTo(city1) < 0 && city2.compareTo(city3) < 0) {
    smallestCity = city2;
} else if (city3.compareTo(city1) < 0 && city3.compareTo(city2) < 0) {
    smallestCity = city3;
} else {
    throw new AssertionError("There is no strict order!");
}

String biggestCity;
if (city1.compareTo(city2) > 0 && city1.compareTo(city3) > 0) {
    biggestCity = city1;
} else if (city2.compareTo(city1) > 0 && city2.compareTo(city3) > 0) {
    biggestCity = city2;
} else if (city3.compareTo(city1) > 0 && city3.compareTo(city2) > 0) {
    biggestCity = city3;
} else {
    throw new AssertionError("There is no strict order!");
}

String middleCity;
if (city1.compareTo(smallestCity) > 0 && city1.compareTo(biggestCity) < 0) {
    middleCity = city1;
} else if (city2.compareTo(smallestCity) > 0 && city2.compareTo(biggestCity) < 0) {
    middleCity = city2;
} else if (city3.compareTo(smallestCity) > 0 && city3.compareTo(biggestCity) < 0) {
    middleCity = city3;
} else {
    throw new AssertionError("There is no strict order!");
}

如果元素相等、第一个元素小于并且大于第二个元素（文档） ，则该方法String#compareTo返回。0< 0> 0

但如前所述，排序算法以更聪明的方式执行这些检查，比较少。所以你应该使用一个。

于 2017-09-20T22:30:34.437 回答