问题
public class Divers {
public static void main(String args[]){
String format = "|%1$-10s|%2$-10s|%3$-20s|\n";
System.out.format(format, "FirstName", "Init.", "LastName");
System.out.format(format, "Real", "", "Gagnon");
System.out.format(format, "John", "D", "Doe");
String ex[] = { "John", "F.", "Kennedy" };
System.out.format(String.format(format, (Object[])ex));
}
}
output:
|FirstName |Init. |LastName |
|Real | |Gagnon |
|John |D |Doe |
|John |F. |Kennedy |
I want the output to be centered. If I do not use '-' flag the output will be aligned to the right.
I did not find a flag to center text in the API.
This article has some information about format, but nothing on centre justify.
回答1:
I quickly hacked this up. You can now use StringUtils.center(String s, int size) in String.format.
import static org.hamcrest.CoreMatchers.*;
import static org.junit.Assert.assertThat;
import org.junit.Test;
public class TestCenter {
@Test
public void centersString() {
assertThat(StringUtils.center(null, 0), equalTo(null));
assertThat(StringUtils.center("foo", 3), is("foo"));
assertThat(StringUtils.center("foo", -1), is("foo"));
assertThat(StringUtils.center("moon", 10), is(" moon "));
assertThat(StringUtils.center("phone", 14, '*'), is("****phone*****"));
assertThat(StringUtils.center("India", 6, '-'), is("India-"));
assertThat(StringUtils.center("Eclipse IDE", 21, '*'), is("*****Eclipse IDE*****"));
}
@Test
public void worksWithFormat() {
String format = "|%1$-10s|%2$-10s|%3$-20s|\n";
assertThat(String.format(format, StringUtils.center("FirstName", 10), StringUtils.center("Init.", 10), StringUtils.center("LastName", 20)),
is("|FirstName | Init. | LastName |\n"));
}
}
class StringUtils {
public static String center(String s, int size) {
return center(s, size, ' ');
}
public static String center(String s, int size, char pad) {
if (s == null || size <= s.length())
return s;
StringBuilder sb = new StringBuilder(size);
for (int i = 0; i < (size - s.length()) / 2; i++) {
sb.append(pad);
}
sb.append(s);
while (sb.length() < size) {
sb.append(pad);
}
return sb.toString();
}
}
回答2:
public static String center(String text, int len){
String out = String.format("%"+len+"s%s%"+len+"s", "",text,"");
float mid = (out.length()/2);
float start = mid - (len/2);
float end = start + len;
return out.substring((int)start, (int)end);
}
public static void main(String[] args) throws Exception{
// Test
String s = "abcdefghijklmnopqrstuvwxyz";
for (int i = 1; i < 200;i++){
for (int j = 1; j < s.length();j++){
center(s.substring(0, j),i);
}
}
}
回答3:
Here's the answer using apache commons lang StringUtils.
Please note that you have to add the jar file to the build path. If you are using maven make sure to add commons lang in the dependencies.
import org.apache.commons.lang.StringUtils;
public class Divers {
public static void main(String args[]){
String format = "|%1$-10s|%2$-10s|%3$-20s|\n";
System.out.format(format, "FirstName", "Init.", "LastName");
System.out.format(format,StringUtils.center("Real",10),StringUtils.center("",10),StringUtils.center("Gagnon",20);
System.out.format(String.format(format, (Object[])ex));
}
}
回答4:
Converted the code found at https://www.leveluplunch.com/java/examples/center-justify-string/ into a handy, small one-line function:
public static String centerString (int width, String s) {
return String.format("%-" + width + "s", String.format("%" + (s.length() + (width - s.length()) / 2) + "s", s));
}
Usage:
public static void main(String[] args){
String out = centerString(10, "afgb");
System.out.println(out); //Prints " afgb "
}
I think it's a very neat solution that's worth mentioning.
回答5:
I was playing around with Mertuarez's elegant answer above and decided to post my version.
public class CenterString {
public static String center(String text, int len){
if (len <= text.length())
return text.substring(0, len);
int before = (len - text.length())/2;
if (before == 0)
return String.format("%-" + len + "s", text);
int rest = len - before;
return String.format("%" + before + "s%-" + rest + "s", "", text);
}
// Test
public static void main(String[] args) {
String s = "abcde";
for (int i = 1; i < 10; i++){
int max = Math.min(i, s.length());
for (int j = 1; j <= max; j++){
System.out.println(center(s.substring(0, j), i) + "|");
}
}
}
}
Output:
a|
a |
ab|
a |
ab |
abc|
a |
ab |
abc |
abcd|
a |
ab |
abc |
abcd |
abcde|
a |
ab |
abc |
abcd |
abcde |
a |
ab |
abc |
abcd |
abcde |
a |
ab |
abc |
abcd |
abcde |
a |
ab |
abc |
abcd |
abcde |
Practical differences from Mertuarez's code:
- Mine does the math up-front and makes the final centered string in one shot instead of making a too-long string and then taking a substring from it. I assume this is slightly more performant, but I did not test it.
- In the case of text that can't be perfectly centered, mine consistently puts it half a character to the left rather than putting it half a character to the right half of the time.
- In the case of text that's longer than the specified length, mine consistently returns a substring of the specified length that's rooted at the beginning of the original text.
回答6:
Here's an example of how I've handled centering column headers in Java:
public class Test {
public static void main(String[] args) {
String[] months = { "January", "February", "March", "April", "May", "June", "July", "August", "September",
"October", "November", "December" };
// Find length of longest months value.
int maxLengthMonth = 0;
boolean firstValue = true;
for (String month : months) {
maxLengthMonth = (firstValue) ? month.length() : Math.max(maxLengthMonth, month.length());
firstValue = false;
}
// Display months in column header row
for (String month : months) {
StringBuilder columnHeader = new StringBuilder(month);
// Add space to front or back of columnHeader
boolean addAtEnd = true;
while (columnHeader.length() < maxLengthMonth) {
if (addAtEnd) {
columnHeader.append(" ");
addAtEnd = false;
} else {
columnHeader.insert(0, " ");
addAtEnd = true;
}
}
// Display column header with two extra leading spaces for each
// column
String format = " %" + Integer.toString(maxLengthMonth) + "s";
System.out.printf(format, columnHeader);
}
System.out.println();
// Display 10 rows of random numbers
for (int i = 0; i < 10; i++) {
for (String month : months) {
double randomValue = Math.random() * 999999;
String format = " %" + Integer.toString(maxLengthMonth) + ".2f";
System.out.printf(format, randomValue);
}
System.out.println();
}
}
}
来源：https://stackoverflow.com/questions/8154366/how-to-center-a-string-using-string-format