java数据类型转换分为哪两种类型(Java数据类型转换方式和原则)

Introduction

In Java, it is common to convert data from one type to another, either implicitly or explicitly.

Java has two types of data conversion: primitive type and object type conversion. In this article, we will discuss the differences between these two types of conversion and how to do it.

Primitive type conversion

Java provides automatic conversion for primitive types. When you assign a value of one primitive data type to another data type, Java automatically converts the value to the target type. This is called widening, which happens when the source type has a smaller range than the target type.

For example, an int can be assigned to a long without any problems because the long data type has a larger range than the int data type. The following example code shows an automatic conversion from int to long.

```java
int num = 10;
long lng = num;
```

However, sometimes we need to perform a narrowing conversion, which happens when the source type has a larger range than the target type. In this case, we need to use an explicit type cast to convert the data type.

For example, if we have a double value and need to assign it to an int variable, we need to use the following code:

```java
double dNum = 10.5;
int iNum = (int) dNum;
```

Object type conversion

Object type conversion happens when we need to convert an object of one type into an object of another type. This is done through upcasting or downcasting.

Upcasting is converting a subclass type to a superclass type. This is done implicitly, without the need for any explicit code. For example:

```java
String str = "Hello";
Object obj = str;
```

In this example, an instance of the String class is upcast to the Object class.

Downcasting is converting a superclass type to a subclass type. This requires an explicit cast because the subclass may have additional methods or fields that the superclass doesn't have. For example:

```java
Object obj = "Hello";
String str = (String) obj;
```

In this example, an instance of the Object class is downcast to the String class.

Conclusion

In conclusion, Java data type conversion is an important concept that we need to understand in order to work with Java programs effectively. There are two types of data conversion: primitive type conversion and object type conversion. We learned that primitive type conversion can be done implicitly or explicitly. On the other hand, object type conversion is done through upcasting or downcasting, depending on the direction of the conversion. Understanding these concepts is crucial for developing high-quality Java programs.