types.md

Types in Java

• Primitive types
• String
  • Formatting strings

Primitive types

8 primitive types and corresponding Wrapper classes (immutable):

• Non-numeric types:

  • boolean (true, false) - 1 Byte (Boolean)
  • char - 2 Bytes (Character)

• Numeric types:

  • byte - 1 Byte (Byte)
  • short - 2 Bytes (Short)
  • int - 4 Bytes (Integer)
  • long - 8 Bytes (Long)
  • float - (Float)
  • double - (Double)

Autoboxing and unboxing when primitive type var used with var of wrapper class.

Special keywords

• void - no return value
• var - auto detected type based on value type (since Java 11)

var i = 1; // 'int' type
var s = "Hello"; // 'String' type

String

String is immutable.

\ - escape character

Formatting strings

String.format() specifiers:

• %s - String
• %d - byte, short, int, long
• %f - double, float
• %b - boolean
• %c - char
• %t - Date
• %% - % chanracter

String str = String.format("a=%3$d, b=%2$d, c=%d", c, b, a);

String Pool

Internal area for storing String literals (deduplication).

Method String.intern() returns reference to String in String Pool.

String s1 = new String("String literal");
String s2 = new String("String literal");
String comparison = String.format("s1 == s2: %b. s1.intern() == s2.intern(): %b", 
    s1 == s2, s1.intern() == s2.intern());
System.out.println(comparison);

Output:
s1 == s2: false. s1.intern() == s2.intern(): true

StringTokenizer

String str = "Alice, Bob, Carol, David";

StringTokenizer tokenizer = new StringTokenizer(str,", ");
while (tokenizer.hasMoreTokens())
{
   String token = tokenizer.nextToken();
   System.out.println(token);
}

StringBuilder

StringBuilder is mutable, it is to be used to overcome String immutable nature.

Popular methods:

• append(), insert(), replace(), delete()
• charAt(), setCharAt(), deleteCharAt()
• substring(), reverse()
• indexOf(), lastIndexOf()
• length()
• toString()

String str = new StringBuilder("Hello world!")
    .replace(6,11, "Universe")
    .toString();

StringBuffer

Similar to StringBuilder, methods of StringBuffer marked as synchronized for use in multithreaded applications.