Basic data Type wrapper class

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I. Basic data type Object wrapper class

A the benefit of encapsulating basic data types into objects is that you can define more functional methods in the object to manipulate the data.

b One of the most common operations: for the conversion between the base data type and the string.

c) For example: Integer Parselnt method, Intvalue method.

D The class used to describe the object is called the basic data type Object wrapper class.

Two. String à basic type

A The use of static methods in the package half class Xxxparsexxx

I. int parseint ("intstring");

Ii. long Parselong ("|longstring");

Iii. boolean Parseboolean ("booleanstring");

IV. Only character have no parse method.

b If the string is encapsulated by an integer.

I. Another non-static method can be used, intvalue ();

Ii. convert an Integer object to the base data type value.

c) integers have different embodiment of the system

I. Decimal à other integer.tobinarystring (60); Integer.tooctalstring (60); Integer.tostring (60,16);

II. Other system à decimal integer.parsenint ("110", 10);

d The integer class Overrides Equals () in object, so the integer object calls the Equals () method when it is a value.

e) simplifies the definition after JDK1.5

I. Integer x = new Integer (4); can be written directly

Ii. Integer x = 4;//Automatic Boxing

Iii. x = x + 5;//automatic unpacking, through the Intvalue method.

f) need to be aware

I. In use, the Integer x =null; The code above will appear nullpointerexception.

II. Automatic boxing, if the boxed is a byte, then the data will be shared without reopening space.

1. Integer = 127;integer = 127; System.out.print (x==y);//true

2. Integer = 128;integer = 128; System.out.print (x==y);//false

Iii. a small to large sort of number for a string.

1. How to get to these values in this string that need to be sorted.

2. A string object may be used to cut a large string into several small strings.

3. The value eventually becomes a small string, and the string becomes the base data type that can use the wrapper class.

Iv. Specific steps:

1. Turn the string into an array of strings String[]str_arr = Numstr.split ("");

2. Convert a string array to an int array int num_arr = Tointarray (Num_arr); create Tointarray (string[) arr); method

3. Sort an array of int

4. Converts a sorted array of int into a string

Three. String class

A The string is a special object

b The string cannot be changed once it is initialized

c) String str = "ABV";

d) String str = new String ("abc"); The string type cannot be changed once it is initialized.

e) The string class is a replication of the Equals method in the object class. This method is used to determine whether the string is the same.