JLS100709：Raw Type(原生类型)

 

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Hist:

100709, draft

 

 

JLS 4.8中是这样定义Raw Type的:

To facilitate interfacing with non-generic legacy code, it is also possible to use as

a type the erasure of a parameterized type. Such a type is called a raw type.

More precisely, a raw type is define to be either:

• The name of a generic type declaration used without any accompanying

actual type parameters.

• Any non-static type member of a raw type R that is not inherited from a superclass

or superinterface of R.

 

意译如下:

为了方便兼容以前代码, 参数化的类型可以不指定参数而使用. 这种不指定参数的参数化类型,就称为raw type. 具体的就是下面两种情况之一:

1)      泛型类型不指定参数, 直接使用的, 是raw type.

2)      raw type的类型R, 它的非static成员(包括成员变量和方法),如果不是继承自R的父类或父接口的化, 也是raw type.

 

具体的例子:

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public class CarColor {     public final static int RED = 1;     public final static int BLUE = 2;     public final static int YELLOW = 3;       public int color;         public String toString(){        switch (color){        case RED:            return "red";        case BLUE:            return "blue";        case YELLOW:            return "yellow";        default:            return "n/a";        }     } }

 

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public class Car {       public static void main(String[] args) {               CarColor color = new CarColor();        color.color = CarColor.RED;               // ok case        Car okCase = new Car(color);        System.out.println("okCase: "+okCase);          // raw type 1 case,        //没有指定类型参数, Car是raw type        Car rawTypeCase = new Car(color);          // raw type 2 case,        // Car是raw type, 所以它的成员setColor()也是raw type.        // 入口参数color不能被编译器检查是否符合类型参数,        // 因为raw type是没有类型参数信息.         rawTypeCase.setColor(color);          System.out.println("rawType1Case: "+rawTypeCase);     }         private T color;       public Car(T color){        this.color = color;     }         public void setColor(T color){        this.color = color;     }         public T getColor(){        return color;     }       public String toString(){        return "The car color is "+color+".";     } }

 

Raw Type的翻译,网络上见到有翻作”未经处理类型”, 比较莫名, 感觉还是”原生类型”更妥帖些, raw type其实就是没有指定类型参数的泛型而已, 原本就是先前泛型没有出现在java时的使用情况。

 

 

REF

1.       JLS 3nd

2.       JVM 2nd