Java - truncate string from left with formatter flag

问题

I have a string, say:

String s = "0123456789";

I want to pad it with a formatter. I can do this two ways:

String.format("[%1$15s]", s); //returns [     0123456789]

String.format("[%1$-15s]", s); // returns [0123456789     ]

if I want to truncate text I do

String.format("[%1$.5s]", s);  // returns [01234]

if I want to truncate from the left, I thought I could do this:

String.format("[%1$-.5s]", s); // throws MissingFormatWidthException

but this failed, so I tried this:

String.format("[%1$-0.5s]", s); // throws MissingFormatWidthException

as well as this:

String.format("[%1$.-5s]", s); // throws UnknownFormatConversionException

So how then do I truncate from the left using a format flag?

回答1:

The - flag is for justification and doesn't seem to have anything to do with truncation.

The . is used for "precision", which apparently translates to truncation for string arguments.

I don't think format strings supports truncating from the left. You'll have to resort to

String.format("[%.5s]", s.length() > 5 ? s.substring(s.length()-5) : s);

回答2:

I hope this is what you need:

System.out.println("'" + String.format("%-5.5s", "") + "'");
System.out.println("'" + String.format("%-5.5s", "123") + "'");
System.out.println("'" + String.format("%-5.5s", "12345") + "'");
System.out.println("'" + String.format("%-5.5s", "1234567890.....") + "'");

output length is always 5:

' ' - filled with 5 spaces
'123 ' filled with 2 spaces after
'12345' - equals
'12345' - truncated

in addition:

System.out.println("'" + String.format("%5.5s", "123") + "'");

output:

' 123' filled with 2 spaces before

回答3:

You could also use method for manipulating Strings

substring(startindex, endIndex)

Returns a string object that starts a the specified index an goes to, but doesn't include, the end index.

And also could try to use StringBuilder class.

来源：https://stackoverflow.com/questions/25630425/java-truncate-string-from-left-with-formatter-flag

标签

java

string-formatting