摆脱最后一个逗号
当我的程序打印出整数5到1时，我需要帮助摆脱最后一个逗号
int i; for (i=10; i>1; --i){ if ( i%2==0) { System.out.print( i/2 + "," ); 打印出5,4,3,2,1,
我希望它打印出5,4,3,2,1
一种有效的方法如下：
StringBuilder stringBuilder = new StringBuilder(); for (i=10; i>1; --i){ if ( i%2==0) { stringBuilder.append(i/2); stringBuilder.append(","); } } stringBuilder.setLength(stringBuilder.length()-1);//remove last comma System.out.println(stringBuilder.toString());
一个简单的if会这样做但更好更有效的方法是使用StringBuilder
int i = 0; for (i = 10; i > 1; --i) { if (i % 2 == 0) { System.out.print(i / 2); if (i > 2) { System.out.print(","); } } }
使用StringBuilder，代码将如下所示
public class Test { public static void main(String[] args) { int i = 0; StringBuilder sb = new StringBuilder(); for (i = 10; i > 1; --i) { if (i % 2 == 0) { sb.append(i / 2).append(","); } } sb.deleteCharAt(sb.length() - 1); System.out.println(sb); }}
有几种不同的方法，例如写入缓冲区，在打印之前删除最后一个逗号，或者另外的if条件，如果i == 2 System.out.print（i / 2）;
这是我使用StringBuilder类的通用解决方案：
/** * @param x Inclusive from-value * @param y Inclusive to-value * @param step Gap between numbers * @param separator What separates the numbers from each other? * @return Numbers from x to y separated by a separator in String format */ public static String integersFromXToYWithSeparator(Integer x, Integer y,Integer step, Character separator) { StringBuilder builder = new StringBuilder(); Integer localStep = Math.abs(step); if (x < y) { while (x <= y) { builder.append(x); builder.append(separator); x+=localStep; } } else if (x > y) { while (x >= y) { builder.append(x); builder.append(separator); x-=localStep; } } builder.setLength(builder.length()-1); return builder.toString(); }
从java-8有一个StringJoiner类可以帮助解决这个问题：
StringJoiner joiner = new StringJoiner(","); for (int i = 10; i > 1; --i) { if (i % 2 == 0) { joiner.add(String.valueOf(i / 2)); } } System.out.println(joiner.toString());
或者使用stream - api
String result = IntStream.iterate(10, i -> i - 1) .limit(10).filter(i -> i % 2 == 0) .map(i -> i / 2) .mapToObj(String::valueOf) .collect(Collectors.joining(",")); System.out.println(result);