問題描述

例如為什么你可以這樣做:

For example why can you do:

int n = 9;

但不是:

Integer n = 9;

你可以這樣做:

Integer.parseInt("1");

但不是:

int.parseInt("1");

推薦答案

int 是原始類型.int 類型的變量存儲您要表示的整數的實際二進制值.int.parseInt("1") 沒有意義，因為 int 不是 一個類，因此沒有任何方法.

int is a primitive type. Variables of type int store the actual binary value for the integer you want to represent. int.parseInt("1") doesn't make sense because int is not a class and therefore doesn't have any methods.

Integer 是一個類，與 Java 語言中的任何其他類沒有什么不同.Integer 類型的變量將 references 存儲到 Integer 對象，就像任何其他引用(對象)類型一樣.Integer.parseInt("1") 是對 Integer 類的靜態方法 parseInt 的調用(注意這個方法實際上返回一個 int 而不是 Integer).

Integer is a class, no different from any other in the Java language. Variables of type Integer store references to Integer objects, just as with any other reference (object) type. Integer.parseInt("1") is a call to the static method parseInt from class Integer (note that this method actually returns an int and not an Integer).

更具體地說，Integer 是一個具有 int 類型的單個字段的類.此類用于需要將 int 視為任何其他對象的情況，例如在泛型類型或需要可空性的情況下.

To be more specific, Integer is a class with a single field of type int. This class is used where you need an int to be treated like any other object, such as in generic types or situations where you need nullability.

請注意，Java 中的每個原始類型都有一個等效的 wrapper 類:

Note that every primitive type in Java has an equivalent wrapper class:

• byte 有 Byte
• short 有 short
• int 有 Integer
• long 有 Long
• boolean 有 Boolean
• char 有 Character
• float 有 Float
• double 有 Double

• byte has Byte
• short has Short
• int has Integer
• long has Long
• boolean has Boolean
• char has Character
• float has Float
• double has Double

包裝類繼承自 Object 類，而原始類不繼承.所以它可以用在帶有對象引用或泛型的集合中.

Wrapper classes inherit from Object class, and primitive don't. So it can be used in collections with Object reference or with Generics.

從 java 5 開始，我們有了自動裝箱，原始類和包裝類之間的轉換是自動完成的.但是要小心，因為這可能會引入細微的錯誤和性能問題；明確說明轉化永遠不會受到傷害.

Since java 5 we have autoboxing, and the conversion between primitive and wrapper class is done automatically. Beware, however, as this can introduce subtle bugs and performance problems; being explicit about conversions never hurts.

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