How to use Wrapper in Java

##1. Overview

Define corresponding reference types - packaging classes (packaging classes) for eight basic data types.

2. Function

With the characteristics of a class, you can call methods in the class. Java is truly object-oriented.

The corresponding relationship between the eight basic data types and their packaging classes:

Basic data typesPackaging classes##byteByteshortShortintIntegerlongLong##float##doubleboolean1. Basic data type-Instance of packaging class (boxing)

Float
Double
Boolean	##char
Character	3. Use

⭕ Implemented through the constructor of the packaging class:

int i = 500; 
Integer t = new Integer(i);

⭕ Constructing the packaging class object through string parameters:

Float f = new Float(“4.56”);
//Long l = new Long(“asdf”); 报错：NumberFormatException

⭕ Error example:

Integer in3 = new Integer("123abc");
System.out.println(in3.toString());
/*  
报错：
Exception in thread "main" java.lang.NumberFormatException: For input string: "123abc"
 */

2. Packaging class - basic Data type (unboxing)

⭕ Call the

xxxValue()

method of the packaging class:

boolean b = bObj.booleanValue();

Note: After

JDK1.5, automatic support is supported Packing, automatic unboxing. But the type must match

3. String-Basic data type/wrapper class

⭕ Implemented through the constructor of the wrapper class:

    int i = new Integer(“12”);

⭕ Through the

of the wrapper class parseXxx(String s)

Static method:

Float f = Float.parseFloat(“12.1”);

⭕ Error example:

int num1 = (int)str1;
Integer in1 = (Integer)str1;
//可能会报NumberFormatException

4. Basic data type/packaging class-String

⭕ Call string heavy Loaded

valueOf()

method:

   String fstr = String.valueOf(2.34f);

⭕ More direct way:

   String intStr = 5 + "";

5. Conversion graph

四、Classic questions

//(1)
     Object o1 = true ? new Integer(1) : new Double(2.0);
     System.out.println(o1);//1.0
     Object o2;
        if (true)
            o2 = new Integer(1);
        else
            o2 = new Double(2.0);
        System.out.println(o2);//1
    }
//(2)
//java
        Integer i = new Integer(1);
        Integer j = new Integer(1);
        System.out.println(i == j);//false
        Integer m = 1;
        Integer n = 1;
        System.out.println(m == n);//true
        Integer x = 128;
        Integer y = 128;
        System.out.println(x == y);//false

The above is the detailed content of How to use Wrapper in Java. For more information, please follow other related articles on the PHP Chinese website!