【问题标题】：How to format String on the left and int on the right?如何格式化左边的String和右边的int？
【发布时间】：2018-03-21 13:21:42
【问题描述】：

我正在尝试从 2 个数组中获取格式化输出，其中一个是国家，另一个是人口，应该提供如下输出：

埃及 | 92592000 法国 | 66991000 日本 | 126860000 瑞士 | 8401120

我收到的唯一提示是我应该计算每列所需的最大宽度，然后使用它来对齐值。这是我迄今为止想出的，但在格式化时坚持要输出任何东西。

public static void main (String[] args) throws java.lang.Exception
{
    String [] countries = {"Egypt", "France", "Japan", "Switzerland"};
    int[] populations = {92592000, 66991000, 126860000, 8401120};
    printTable(countries, populations);
}

public static void printTable(String[] countries, int[] populations){
    int longestInput = 0;
    for(int i = 0; i < countries.length; i++){
        int countLength = countries[i].length();
        int popLength = String.valueOf(populations[i]).length();
        if(countLength + popLength > longestInput)
            longestInput = countLength + popLength;
    }

    for(int i = 0; i < countries.length; i++)
    System.out.format("%-10",countries[i] + " | " + populations[i]);
}

【问题讨论】：

您需要计算两个最大长度：国家和人口。然后你用最长的国家填充每个国家，用最长的流行填充每个人口，加入这些字符串并打印它们。
为什么你的 main 抛出 java.lang.Exception？
它是因为我尝试在底部格式化，如果我删除其他所有工作，或者可能来自导入 java.util.*；导入java.lang.*；导入java.io.*；我忘记放入sn-p
这是否意味着有例外？我认为您必须在格式中添加“转换”。看this answer。
看起来它可以帮助我现在尝试一下，我只有在尝试格式化输出时才会出现异常，因为如果我不正常工作

标签： java format formatter

【解决方案1】：

这是一个小例子：

public static void main (String[] args) throws java.lang.Exception
  {
    String [] countries = {"Egypt", "France", "Japan", "Switzerland"};
    int[] populations = {92592000, 66991000, 126860000, 8401120};
    printTable(countries, populations);
  }

  public static void printTable(String[] countries, int[] populations){
    int countryLength = 0;
    long populationLength = 0;

    for(String country: countries){ //get longest country
      if (country.length() > countryLength)
        countryLength = country.length();
    }
    for(int i : populations) { //get longest number
      if(String.valueOf(i).length() > populationLength)
        populationLength = String.valueOf(i).length();
    }

    for(int i = 0; i < countries.length; i++) // print it out
      System.out.format("%-"+ (countryLength+1) +"s|%" + (populationLength+1) +"d\n",countries[i], populations[i]);
  }

首先获得最长的国家：

for(String country: countries){ //get longest country
  if (country.length() > countryLength)
    countryLength = country.length();
}

其次用String.valueOf(i).length()得到最长的人口：

for(int i : populations) { //get longest number
  if(String.valueOf(i).length() > populationLength)
    populationLength = String.valueOf(i).length();
}

最后用System.out.format打印出来：

System.out.format("%-"+ (countryLength+1) +"s|%" + (populationLength+1) +"d\n",countries[i], populations[i]);

【讨论】：

【解决方案2】：

使用 Java 8

public static void main (String[] args) throws java.lang.Exception {
    String [] countries = {"Egypt", "France", "Japan", "Switzerland"};
    int[] populations = {92592000, 66991000, 126860000, 8401120};
    printTable(countries, populations);
}

public static void printTable(String[] countries, int[] populations) {
    if (countries.length == 0 || populations.length == 0 || countries.length != populations.length) {
        return;
    }
    int longestCountry = Arrays.stream(countries)
            .map(String::toString)
            .mapToInt(String::length)
            .max()
            .getAsInt();
    int longestPop = Arrays.stream(populations)
            .mapToObj(Integer::toString)
            .mapToInt(String::length)
            .max()
            .getAsInt();

    for (int i = 0; i < countries.length; i++) {
        System.out.printf("%-" + longestCountry + "s | %" + longestPop + "d%n", 
            countries[i], 
            populations[i]);
    }
}

诀窍是使用流来获取长度并使用负格式字符串填充字符串的右侧。

【讨论】：

如果countries 或population 为空数组，您的方法可能会引发异常
添加了检查，我假设两者都不会为空以简化代码

【解决方案3】：

您可能正在寻找的模式是：

"%-" + maxCountryLength + "s | %" + maxPopulationLength + "d\n"

%-Xs 表示“X 字符宽度，左对齐 String”
%Xd 表示“X 字符宽度，右对齐数字”
\n 表示占一行

该方法可能如下所示：

public static void printTable(String[] countries, int[] populations) {
    int defaultLength = 10;
    int maxCountryLength = stream(countries).mapToInt(String::length).max().orElse(defaultLength);
    int maxPopulationLength = stream(populations).mapToObj(Integer::toString).mapToInt(String::length).max().orElse(defaultLength);

    for (int i = 0; i < countries.length; i++) {
        System.out.format("%-" + maxCountryLength + "s | %" + maxPopulationLength + "d\n", countries[i], populations[i]);
    }
}

结果：

Egypt       |  92592000
France      |  66991000
Japan       | 126860000
Switzerland |   8401120

【讨论】：

【解决方案4】：

我重写了 printTable 方法，效果很好：

public static void printTable(String[] countries, int[] populations)
{
    if(countries.length != 0)
    {

        int longestNameInput = countries[0].length();
        int longestPopInput = String.valueOf(populations[0]).length();

        for(int i = 0; i < countries.length; i++)
        {
            int countLength = countries[i].length();
            int popLength = String.valueOf(populations[i]).length();

            if(countLength > longestNameInput)
                longestNameInput = countLength;

            if(popLength > longestPopInput)
                longestPopInput = popLength;
        }

        for(int i = 0; i < countries.length; i++)
        {
            System.out.print(countries[i]);
            for(int j = 0; j < (longestNameInput - countries[i].length()); j++)
                System.out.print(" ");
            System.out.print(" | ");

            for(int k = 0; k < (longestPopInput - String.valueOf(populations[i]).length()); k++)
                System.out.print(" ");
            System.out.println(populations[i]);
        }

    }
}

【讨论】：

【解决方案5】：

public static void main (String[] args) throws java.lang.Exception {
    String [] countries = {"Egypt", "France", "Japan", "Switzerland"};
    Integer[] populations = {92592000, 66991000, 126860000, 8401120};
    printTable(countries, populations);
}

public static void printTable(String[] countries, Integer[] populations){
    int longestInput = 0;
    for(int i = 0; i < countries.length; i++){
        int countLength = countries[i].length();
        int popLength = String.valueOf(populations[i]).length();
        if(countLength + popLength > longestInput)
            longestInput = countLength + popLength;
    }

    String longestString = getLongestString( countries );
    System.out.format("longest string: '%s'\n", longestString);

    Integer longestNumber = getLongestNumber( populations );
    System.out.format("longest Number: '%s'\n", longestNumber);

    for(int i = 0; i < countries.length; i++)
        System.out.format("%-" + longestString.length() + "s | %" + String.valueOf(longestNumber).length() + "d\n", countries[i], populations[i]);

}

在字符串数组中查找最长的字符串

public static String getLongestString(String[] array) {
    int maxLength = 0;
    String longestString = null;
    for (String s : array) {
        if (s.length() > maxLength) {
            maxLength = s.length();
            longestString = s;
        }
    }
    return longestString;
}

在整数数组中查找最长的数字

public static Integer getLongestNumber(Integer[] array) {
    int maxLength = 0;
    Integer longestNumber = null;
    for (Integer i : array) {
        if (String.valueOf(i).length() > maxLength) {
            maxLength = String.valueOf(i).length();
            longestNumber = i;
        }
    }
    return longestNumber;
}

输出«

longest string: 'Switzerland'
longest Number: '126860000'
Egypt       |  92592000
France      |  66991000
Japan       | 126860000
Switzerland |   8401120

【讨论】：