wrapperclassdemo.java

JAVA程序设计课程中各章节的程序实例。

/**
*A Wrapper class demonstration program
*2004.12.27.xhcprince
*/

class WrappedClassDemo
{
	public static void main(String args[])
	{
		/*-------------------------------------------------------------------------
		  A wrapper class object is constructed by passing the value to the wrapped
		  into the appropriate constructor
		  Each primitive data has a corresponding wrapper class
		-------------------------------------------------------------------------*/
		int ptyp = 10;
		Integer pobj = new Integer(ptyp);
		System.out.println(pobj);
		
		
		
		Integer x = new Integer(10);
		int i = x + 16;
		/*-------------------------------------------------------------------------
		  Note that the second line of the above code smippet is incorrect
		  The corrsct way to add an integer value with the one wrapped inside a 
		  class is as follows:
		  (strangely there's no compile error in my computer?!)
		-------------------------------------------------------------------------*/ 
		int j = x.intValue() + 16;
		
		System.out.println(i);
		
		
		
		/*-------------------------------------------------------------------------
		  The wrapper classes have another important function,which is to group 
		  together a set of methods that operate on actual primitive types
		-------------------------------------------------------------------------*/
		int t = 123456;
		String t1 = Integer.toHexString(t);
		String t2 = Integer.toOctalString(t);
		String t3 = Integer.toBinaryString(t);
		
		System.out.println(t1);
		System.out.println(t2);
		System.out.println(t3);
		
		
		
		/*-------------------------------------------------------------------------
		  Wrapper classes also contain methods for converting primitive types to
		  Strings and vice versa
		-------------------------------------------------------------------------*/
		Double temp = new Double("11.66");
		double result = temp.doubleValue();
		
		System.out.println(result);
		
		
		
		/*-------------------------------------------------------------------------
		  Wrapper classes also define constants for a given primitive type
		-------------------------------------------------------------------------*/
		System.out.println(Byte.MAX_VALUE);
		System.out.println(Character.MAX_VALUE);//why the output is "??".
//		System.out.println(Boolean.MAX_VALUE); //there's no MAX_VALUE in Boolean!
		System.out.println(Short.MAX_VALUE);
		System.out.println(Integer.MAX_VALUE);
		System.out.println(Long.MAX_VALUE);
		System.out.println(Float.MAX_VALUE);
		System.out.println(Double.MAX_VALUE);
		
		
		
		/*-------------------------------------------------------------------------
		  Wrapper classes have some other useful methods such as follows:
		  
		  parseInt():takes a String argument and returns the corresponding int.
		  toString():converts an int argument to String
		  (also the same with Double,Long,Short,Float...)
		  
		  isInfinite():returns true if the value being tested is infinitely 
		  			   large or small magnitude
		  isNaN():returns true if the value being tested is not! a number
		  		  NaN refers to "Not an Number"!		  	   
		-------------------------------------------------------------------------*/
		String s1 = "111";
		int i1 = Integer.parseInt(s1);
		
		System.out.println(i1);
		
		int i2 = 666;
		String s2 = Integer.toString(i2);
		
		System.out.println(i2);
		
		Double d1 = new Double(1/0.);
		Double d2 = new Double(0/1.);
		
		System.out.println(d1.isInfinite() + " " + d1.isNaN());
		System.out.println(d2.isInfinite() + " " + d2.isNaN());
		
		
		
		/*-------------------------------------------------------------------------
		  I'd like to omit the demonstration of some methods such as:
		  isDigit(),isLetter(char),isLetter(),isWhiteSpace(),
		  isLowerCase(),isupperCase()
		  toLowerCase(),toUpperCase().
		--------------------------------------------------------------------------*/
	}
}