Confusion for Java Beginners: The Mystery of Variable Type Conversion

Variable type conversion in Java refers to converting one data type to another. There are two types of conversion: 1. Implicit conversion: performed automatically, converting a smaller type to a larger type. 2. Explicit conversion: Use the cast operator to explicitly specify the conversion. Methods such as String.valueOf() and Integer.parseInt() can be used to convert between numeric types and strings. Object type conversion can be achieved through inheritance, interfaces or type conversion.

Java Beginner’s Confusion: The Mystery of Variable Type Conversion

In Java, variable type conversion refers to converting a data Convert data of one type to another data type. This is very convenient when working with data between different data types.

Implicit type conversion and explicit type conversion

Java mainly has two types of type conversion:

• Implicit Type conversion (automatic conversion): The Java compiler will automatically perform conversion of certain data types. For example, converting from a smaller data type (such as byte) to a larger data type (such as int).
• Explicit type conversion (forced conversion): You need to explicitly use syntax to convert one data type to another data type. For example, when you need to convert int to byte, you need to use the cast operator (byte).

Conversion between basic types

The basic data types in Java and their compatible conversions are as follows:

byte → short → char → int → long → float → double

Conversion between numeric types and strings

• Convert numeric types to strings: You can use the String.valueOf() method. For example:

int i = 10;
String s = String.valueOf(i);

• Convert string to numeric type: You can use Integer.parseInt(), Long.parseLong( ) and other methods. For example:

String s = "123";
int i = Integer.parseInt(s);

Conversion between object types

Conversion between object types can be achieved through inheritance, interfaces or type conversion. For example, you can use the instanceof operator to check whether an object belongs to a class.

Practical Case

Consider a program that needs to calculate student scores. Student grades can be floating point numbers, but ultimately need to be stored as integers.

float score = 95.5f;

// 将 float 转换为 int（强制类型转换）
int roundedScore = (int) score;

// 检查舍入后的分数是否为 A
if (roundedScore >= 90) {
    System.out.println("优秀");
}

By using cast, we can conveniently round floating point numbers to integers and use them for integer operations.

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