Strings

A string literal is represented by sequence of characters in double quotes.

The String class implements immutable string. Most JVM are cahing string values, but not always.

The StringBuilder class implements mutable string. It is used hiddenly in expressions with string concatenation by the + operator. So do not use + with strings in a long loop. Instead, create a StringBuilder before the loop, and then use it inside.

The StringBuffer class is a thread-safe version of StringBuilder.

All mentioned classes implements the CharSequence interface.

The StringJoiner class is used to construct a sequence of characters separated by a delimiter. Optionally, you can specify a prefix and suffix.

String str = "my string";
String str1= "a" + "b"; // result "ab", StringBuilder is used

StringBuilder sb = new StringBuilder()
    .append("sb ");
// ...     
sb.append("blablabla");
String str3 = sb.toString();

StringJoiner sj = new StringJoiner(",","(",")");
for(String item: mystrings){
    sj.add(item)
}
// result is string such "(item1,item2,...,itemn)"
String str4 = sj.toString();

if("m".equals(mystr)){...} // don't compare strings with == operator

escape sequences

CharSequence interface

String