Understanding Java Numbers and Strings: Types and Examples

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質問：

Introduce Java Numbers and Strings, and give examples

回答：

In Java, numbers and strings are fundamental data types that are used to represent numerical values and sequences of characters, respectively. Understanding how to work with these types is essential for any Java programmer.

Java Numbers

Java provides several built-in data types for representing numbers, which can be categorized into two main groups: integers and floating-point numbers.

  1. Integer Types:

    • byte: 8-bit signed integer. Range: -128 to 127.
    • short: 16-bit signed integer. Range: -32,768 to 32,767.
    • int: 32-bit signed integer. Range: -2^31 to 2^31-1.
    • long: 64-bit signed integer. Range: -2^63 to 2^63-1.

    Example:

    int age = 30;
long population = 7800000000L; // 'L' suffix indicates a long literal

  2. Floating-Point Types:

    • float: 32-bit single-precision floating-point.
    • double: 64-bit double-precision floating-point.

    Example:

    float temperature = 36.6f; // 'f' suffix indicates a float literal
double pi = 3.14159;

Java Strings

A string in Java is a sequence of characters, and it is represented by the String class. Strings are immutable, meaning once a string is created, it cannot be changed. You can create strings using double quotes.

Example:

String greeting = "Hello, World!";
String name = "Alice";

Common Operations with Numbers and Strings

  1. Arithmetic Operations: You can perform arithmetic operations on numeric types using standard operators (+, -, *, /, %).

    Example:

    int sum = 10 + 20; // sum is 30
double average = (10.0 + 20.0) / 2; // average is 15.0

  2. String Concatenation: You can concatenate strings using the + operator.

    Example:

    String fullName = name + " Smith"; // fullName is "Alice Smith"

  3. String Methods: The String class provides various methods for manipulating strings, such as length(), charAt(), substring(), and toUpperCase().

    Example:

    int length = greeting.length(); // length is 13
char firstChar = greeting.charAt(0); // firstChar is 'H'
String upperGreeting = greeting.toUpperCase(); // upperGreeting is "HELLO, WORLD!"

Conclusion

Java's number and string types are essential for performing calculations and handling text data. By understanding how to use these types and their associated operations, you can effectively manage data in your Java applications.

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