Java - String

About

Text - String in Java.

Class: javase/9/docs/api/java/lang/String.html

Management

Initialization

From a byte array

from a Java - Byte

new String(myByteArray, "UTF-8");

From a array of characters

Arrays.toString("Hello, World!".toCharArray())

From a collection of character

StringBuilder stringBuilder = new StringBuilder();
stringBuilder.append(charactersList);
return stringBuilder.toString();

Construction of large String

• A StringWriter is A character stream that collects its output in a string buffer, which can then be used to construct a string.
• StringBuilder

Join

• The string join method on array

String str = String.join(",", arr);

• or with a stream and the Collectors.joining function

// Example a list of column names join with a comma delimiter 
String columnStatement = IntStream.range(0,source.getDataDef().getColumnDefs().size())
                    .mapToObj(i->source.getDataDef().getColumnDef(i).getColumnName())
                    .collect(Collectors.joining(", "));

Multiplication

• 10 character A

final int generation = 10;
String multi = new String(new char[generation]).replace("\0", "A");
System.out.println(multi);

AAAAAAAAAA

File

With Java - (Nio|New I/O) Package

// Write
Files.write(path, query.getBytes());
// Read
new String(Files.readAllBytes(path));

toCharacter

• Stream: Example when calculating the number of digits

// THe trick is that s.chars() returns characters as int
Math.toIntExact(s.chars()
    .filter(i->Character.isDigit((char) i)))
    .count())

• For

for (int i = 0; i < s.length(); i++){
    char c = s.charAt(i);        
    //Process char
}

toUpperCase

import static java.util.Locale.ENGLISH;
tableName = tableName.toUpperCase(ENGLISH);

Replace with regexp pattern

• How to replace a string with a pattern object.

Pattern pattern = Pattern.compile("pattern");
String replaced = pattern.matcher(text).replaceFirst("");