Lang packet Knowledge point (i) lang Package and packaging class

Lang Package Introduction: 1, Java.lang package is a Java built in a basic package, which contains a series of programs often used in the class; 2,by default, each Java program imports the package automatically, so you do not need to explicitly specify it in your program. package classes in the Lang package:Java provides a series of wrapper classes to manipulate raw data types as objects. In the Java.lang package, there is an appropriate wrapper class for each raw data type.

Each wrapper class has a the static valueof methodThat is used to string into the appropriate wrapper classThe object.

    // If the conversion fails, a NumberFormatException exception    will be thrown String str = "+";     = byte.valueof (str);     = short.valueof (str);     = integer.valueof (str);     = long.valueof (str);

In addition to the Boolean and character classes, other wrapper classes have a static Parsexxx method (XXX refers to a specific data type), which is used to convert the string to the corresponding raw data type value .

     The pasexxx method of each wrapper class is called separately to convert the string, and if the conversion fails, the exception    is reported int i = integer.parseint (str);      Short s = short.parseshort (str);     byte b = byte.parsebyte (str);     long L = long.parselong (str);     float f = float.parsefloat (str);     double d = double.parsedouble (str);

Common methods in the character class

BooleanIsletter (CharCh//determine if the character ch is an English letterBooleanIsDigit (CharCh//determines whether the character Ch is a number between 0~9BooleanIsuppercase (CharCh//determines if the character ch is in uppercase formBooleanIslowercase (CharCH)//determines if the character ch is in lowercase formBooleanIswhitespace (CharCh//determine if the character ch is a space or line break//The above methods are static methods, can be called directly through the class name, the return value isis a Boolean, or False if True is returned.

Title:

There are character arrays: char[] Chararray = {' * ', ' 7 ', ' B ', ', ' A '}; What are each character, respectively?

 Public classCharacterdemo { Public Static voidMain (string[] args) {Char[] Chararray = {' * ', ' 7 ', ' B ', ', ' A '};  for(inti = 0; i < chararray.length; i++) {      if(Character.isdigit (Chararray[i])) {System.out.println (Chararray[i]+ "is a number. "); }      if(Character.isletter (Chararray[i])) {System.out.println (Chararray[i]+ "is a letter. "); }      if(Character.iswhitespace (Chararray[i])) {System.out.println (Chararray[i]+ "is a space. "); }      if(Character.islowercase (Chararray[i])) {System.out.println (Chararray[i]+ "is the lowercase form. "); }      if(Character.isuppercase (Chararray[i])) {System.out.println (Chararray[i]+ "is in uppercase form. "); }    }  }}

Lang packet Knowledge point (i) lang Package and packaging class