java

In this category there are examples of code and articles on java.
Choose the section you need and start learning programming.

java

How to convert java string array to string with delimiter

- by Tirex - Leave a Comment

Using String.join method (from java 8)

1
2
String[] array = new String[] { "a", "b", "c" };
String joined2 = String.join(",", array);

Using simple for-loop expression

1
2
3
4
5
6
StringBuilder sb = new StringBuilder();
for (String n : name) {
    if (sb.length() > 0) sb.append(',');
    sb.append("'").append(n).append("'");
}
return sb.toString();

 

Read More
java

How to convert an int to a formatted string in java

- by Tirex - Leave a Comment

Using java.util.formatter

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
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.

Read More
java

How to check If a String is an Integer in Java

- by Tirex - Leave a Comment

Suppose we have the following problem. User input some value, how to check that this value is a String is an integer: 1. Check by Exception

Java
1
2
3
4
5
6
7
8
9
10
11
12
public static void main(String[] args) {
    System.out.println("Is int? " + IsIntCheckByException("12"));
}
 
private static boolean IsIntCheckByException(String str) {
    try {
        Integer.parseInt(str);
        return true;
    } catch (NumberFormatException nfe) {
        return false;
    }
}

Read More
java

Output data to excel file by template with jxls

- by Tirex - 2 Comments.

Let’s assume we have a Java collection of Car objects that we want to output into Excel. The Car class may look like this

1
2
3
4
5
6
public class Car {
  private String brand;
  private BigDecimal price;
  // ... constructors
  // ... getters/setters
}

To use Jxls to output …

Read More
java

How to repeat string ‘n’ times in java?

- by Tirex - Leave a Comment

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

1
2
3
4
5
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

1
2
3
4
String s = "qwe";
int n = 3;
//this line print 'qweqweqwe'
String newString = String.format("%0" + n + "d", 0).replace("0", s);

Let us examine …

Read More
java

How to convert ‘ArrayList to String array in Java

- by Tirex - Leave a Comment

Using Collection.toArray method First way to convert arraylist is to use built-in for every java collection method toArray(T[] ts) For example:

1
2
3
4
5
6
List<String> animals = new ArrayList<String>();
//add some elements
animals.add("cat");
animals.add("dog");
String[] stringArray = animals.toArray(new String[0]);
System.out.println(Arrays.toString(stringArray));

The toArray()  method without any argument returns Object[].  So you have …

Read More