1. Avoid using strings as substitutes for other data types:

Strings are designed to represent text, but are often misused to represent numbers, enums, or aggregate structures.
If the data is numeric in nature, use types such as int, float or BigInteger, not String.

String age = "30";  // incorreto
int age = 30;       // correto

2. Strings are poor substitutes for enum types:

Using enum is safer and more readable than using strings to represent enumerated values.

String status = "ACTIVE";  // incorreto
Status status = Status.ACTIVE;  // correto, usando enum

3. Strings are inferior substitutes for aggregate types:

Representing complex data as a single string, separated by delimiters, can cause errors and maintenance issues. It is better to create classes for this data.

Incorrect example (use of string to represent aggregated data):

String personData = "John|Doe|30";

Correct example (use of a class):

class Person {
    String firstName;
    String lastName;
    int age;

    // Construtor e métodos adequados
}

4. Strings as substitutes for resources (Example: thread local variables):

Using strings to identify resources as thread-local variables can lead to security issues and name collisions. Replace with more secure keys.

Incorrect example (use of string to identify thread local variable):

Map threadLocalVariables = new HashMap();
threadLocalVariables.put("myVariable", value);

Correct example (use of a secure key):

class Key {
    // implementação da chave
}

Map threadLocalVariables = new HashMap();
Key key = new Key();
threadLocalVariables.put(key, value);

Correct use of ThreadLocal:

The ideal design for thread local variables involves the use of ThreadLocal, which allows the creation of variables associated with each thread in a typesafe manner.

Example of correct use of ThreadLocal:

private static final ThreadLocal threadId = ThreadLocal.withInitial(() -> 0);

public static void main(String[] args) {
    System.out.println(threadId.get());  // obtem o valor da variável local da thread
}

Conclusion:

Avoid the temptation to use strings for everything. Using more appropriate data types or creating new types prevents errors, improves readability, and makes code more efficient and secure.

Examples from the book: