016-Use of packaging

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1. In Java, define the corresponding reference type for the eight basic data types— -Packaging class (encapsulation class), with the characteristics of the class, you can call the method in the class, Java is the real object-oriented.

2. The basic data types are packaged into the instance of the packaging class (boxing).
1. Realized by the constructor of the packaging class:
int i = 500; Integer t = new Integer(i);
2. The packaging class can also be constructed through string parameters Object:
Float f = new Float("4.56");
Long l = new Long("asdf"); //NumberFormatException
3. Obtain the basic type variables of the package in the package object (unboxing) and
call the .xxxValue( of the package class ) Method:
boolean b = bObj.booleanValue();
After JDK1.5, automatic boxing and automatic unboxing are supported, but the types must match.
Fourth, the string is converted into a basic data type
1. Realized by the constructor of the packaging class:
int i = new Integer("12");
2. Through the parseXxx(String s) of the packaging class:
Float f = Float.parseFloat(" 12.1”);
Five, basic data types are converted into strings
1. Call the valueOf() method of string overload:
String fstr = String.valueOf(2.34f);
2. A more direct way:
String intStr = 5 + “”;
6. Example
int i = 500;
Integer t = new Integer(i);//Boxing, making a basic data type of data into the class
String s = t.toString(); //s=”500”, t is the class, there is a toString method
String s1 = Integer .toString(314); //s1=”314” Convert a number to a string
String s2 = “4.56”;
double ds = Double.parseDouble(s2); //Convert a string to a number
int j = t.intValue (); //j=500, intValue takes out the data
packaging class in the package class. The most used in actual development is that the string becomes the basic data type
String str1 = "30";
String str2 = "30.3";
int x = Integer.parseInt(str1);
float f = Float.parseFloat(str2);