Tag: string

How to convert java string array to string with delimiter

Using String.join method (from java 8)

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String[] array = new String[] { "a", "b", "c" };
String joined2 = String.join(",", array);

Using simple for-loop expression

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StringBuilder sb = new StringBuilder();
for (String n : name) {
    if (sb.length() > 0) sb.append(',');
    sb.append("'").append(n).append("'");
}
return sb.toString();

 

How to convert an int to a formatted string in java

Using java.util.formatter

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StringBuilder sb = new StringBuilder();
// Send all output to the Appendable object sb
Formatter formatter = new Formatter(sb, Locale.US);
 
// Explicit argument indices may be used to re-order output.
formatter.format("%4$2s %3$2s %2$2s %1$2s", "a", "b", "c", "d")
// -> " d  c  b  a"
 
// Optional locale as the first argument can be used to get
// locale-specific formatting of numbers.  The precision and width can be
// given to round and align the value.
formatter.format(Locale.FRANCE, "e = %+10.4f", Math.E);
// -> "e =    +2,7183"
 
// The '(' numeric flag may be used to format negative numbers with
// parentheses rather than a minus sign.  Group separators are
// automatically inserted.
formatter.format("Amount gained or lost since last statement: $ %(,.2f",
            balanceDelta);
// -> "Amount gained or lost since last statement: $ (6,217.58)"

See the Formatter docs for other modifiers.

How to repeat string ‘n’ times in java?

Suppose you have the string ‘qwe’ and you need to repeat string ‘n’ times. Here’s how to do it:

Using java 8 stream api

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String newString = Collections.nCopies(3, "qwe").stream().collect(Collectors.joining(""));
 
String newString = Stream.generate(() -> "qwe").limit(3).collect(Collectors.joining());
 
String newString = String.join("", Collections.nCopies(n, s));

Using String.format

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String s = "qwe";
int n = 3;
//this line print 'qweqweqwe'
String newString = String.format("%0" + n + "d", 0).replace("0", s);

Let us examine this example in more detail. Primitive types ( char[] , in this case) are instantiated with nulls “number of times”, then a String is created from the char[] , and the nulls are replaced() with the original string str.

Using StringBuilder and loop

And last but not least, you can use StringBuilder and loop

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int n = 3;
String in = "qwe";
 
StringBuilder b = new StringBuilder(n * in.length());
   for (int i = 0; i < n; i += 1) {
   b.append(in);
}
String newString = b.toString();

Using third-party libraries

You could use Apache commons-lang (which has an impressive collection of handy string utilities):

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String newString = StringUtils.repeat(3, "qwe");

 

How to compare strings in Java?

Test strings equality

==  tests object references, .equals()  tests the string values.

Sometimes it looks as if == compares values, because Java does some behind-the-scenes stuff to make sure identical in-line strings are actually the same object.

For example:

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String fooString1 = new String("foo");
String fooString2 = new String("foo");
 
// Evaluates to false
fooString1 == fooString2;
 
// Evaluates to true
fooString1.equals(fooString2);
 
// Evaluates to true, because Java uses the same object
"bar" == "bar";

Correct null handling

== handles null strings fine, but calling .equals() from a null string will cause an exception:

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String nullString1 = null;
String nullString2 = null;
 
// Evaluates to true
nullString1 == nullString2;
 
// Throws an Exception
nullString1.equals(nullString2);