2015-09-10日问题

 1  /**
 2      * Returns the string representation of the <code>boolean</code> argument.
 3      *
 4      * @param   b   a <code>boolean</code>.
 5      * @return  if the argument is <code>true</code>, a string equal to
 6      *          <code>"true"</code> is returned; otherwise, a string equal to
 7      *          <code>"false"</code> is returned.
 8      */
 9     public static String valueOf(boolean b) {
10         return b ? "true" : "false";
11     }

 1 public class Person
 2 {
 3     public static void main(String[] args) {
 4         
 5         String intstr="123";//装箱：将string类型数据赋值给包装类变量intstr？？？更准确的说法是：将常量池中对象（"123"）的引用赋值给String类型的引用变量intstr.
 6         System.out.println("装箱后="+intstr);//怎么输出结果是整形的？不是字符串类型的么？？？
 7         int it1=Integer.parseInt(intstr);//将intstr转换为int类型的？？因为intstr是String类的变量，为何不是String.parseInt(intstr)？？？
 8         int it2=new Integer(intstr);//这是创建一个对象new Integer()，那new Integer(intstr)是向Integer构造方法中传一个整形instr?但是它的构造方法具体是什么，传参之后是怎么执行的怎么能知道?这里intstr是包装类，怎么能传入一个包装类作为一个实参来传参呢??
 9         System.out.println(it2);
10         String floatstr="456";
11         float ft1=Float.parseFloat(floatstr);//将floatstr转换为Float类型的？？？
12         float ft2=new Float(floatstr);//???
13         System.out.println(ft2);
14         String ftstr=String.valueOf(2.345f);
15         System.out.println("ftstr="+ftstr);
16         String dbstr=String.valueOf(3.344);
17         System.out.println("dbstr="+dbstr);
18         String boolstr=String.valueOf(true);
19         System.out.println("bool+"+boolstr.toUpperCase());
20          //TRUE是string变量？？？？
21     }
22 }

 1  /**
 2      * Prints a String and then terminate the line.  This method behaves as
 3      * though it invokes <code>{@link #print(String)}</code> and then
 4      * <code>{@link #println()}</code>.
 5      *
 6      * @param x  The <code>String</code> to be printed.
 7      */
 8     public void println(String x) {
 9         synchronized (this) {
              //输出这个字符串到控制台
10             print(x);
             //换行
11             newLine();
12         }
13     }

 1  /**
 2      * Constructs a newly allocated {@code Integer} object that
 3      * represents the {@code int} value indicated by the
 4      * {@code String} parameter. The string is converted to an
 5      * {@code int} value in exactly the manner used by the
 6      * {@code parseInt} method for radix 10.
 7      *
 8      * @param      s   the {@code String} to be converted to an
 9      *                 {@code Integer}.
10      * @exception  NumberFormatException  if the {@code String} does not
11      *               contain a parsable integer.
12      * @see        java.lang.Integer#parseInt(java.lang.String, int)
13      */
14     public Integer(String s) throws NumberFormatException {
15         this.value = parseInt(s, 10);
16     }