e058. wrapping a primitive type in a wrapper object.txt

来自「这里面包含了一百多个JAVA源文件」· 文本 代码 · 共 24 行

In the Java language, the eight primitive types --- boolean, byte, char, short, int, long, float, double --- are not objects. However, in certain situations, objects are required. For example, collection classes such as Map and Set only work with objects. This issue is addressed by wrapping a primitive type in a wrapper object. There is a wrapper object for each primitive type. 
This example demonstrates how to wrap the value of a primitive type in a wrapper object and then subsequently retrieve the value of the primitive type. 

    // Create wrapper object for each primitive type
    Boolean refBoolean = new Boolean(true);
    Byte refByte = new Byte((byte)123);
    Character refChar = new Character('x');
    Short refShort = new Short((short)123);
    Integer refInt = new Integer(123);
    Long refLong = new Long(123L);
    Float refFloat = new Float(12.3F);
    Double refDouble = new Double(12.3D);
    
    // Retrieving the value in a wrapper object
    boolean bool = refBoolean.booleanValue();
    byte b = refByte.byteValue();
    char c = refChar.charValue();
    short s = refShort.shortValue();
    int i = refInt.intValue();
    long l = refLong.longValue();
    float f = refFloat.floatValue();
    double d = refDouble.doubleValue();