Examples of knowledge points in java-javaTutorial-php.cn

Examples of knowledge points in java

零下一度

Release： 2017-06-25 11:01:09

Original

1349 people have browsed it

java annotation document

Some commonly usedjavadoctags

##{@inheritDoc}Inherit relevant documents from the most direct base class of the current class into the current document comment@version version-information @author author-information#

Class related

Composition of classes:

Use an object of existing class A as The member variable ( of the new class B usually limits the object of the class A to private)

class A {}public class B {

    Private A a;

}

Copy after login

A,BThe relationship can be determined as ”has-a”(有 )Relationship, means B owns A

Inheritance from class

Existing base classA, ClassBInherited from classA, then class A also becomes the parent class of class B

class A {}class B extends A {}

Copy after login

The relationship between class A and class B can be determined as ”is-a”(是A ) relationship , means B is a A

Override(overwrite)and overload

Overwriting refers to the relationship between the parent class and the subclass. ,The subclass overrides a method of the parent class,and the method name,Return value,Parameter type,Number of parameters,Parameters,are in the same order.

Overloading is in a class,There are multiple methods with the same method name,Their return values,Parameter types,Number of parameters,Parameters,The order must be at least one different .

class A {public void helloWorld() {
    
        System.out.println(“hello world”);
    }
}class B extends A {//重写(覆盖)父类方法public void helloWorld() {
    
        System.out.println(“hello world”);
    
    } 
    public void hi() {
    
        System.out.println(“hi”);
    
    }    //重载上一个方法public int hi() {
    
        System.out.println(“hi”);        return 1;
    }
}

Copy after login

java.lang类默认会被导入java文件中

static修饰的方法或变量属于类,不属于类的对象.static对每个类来说只有一个存储空间,而每个对象都有一个存储空间.可通过staticMethod, 类名.staticMethod, 对象变量.staticMethod等来访问.

创建对象时注意

String s;    //创建引用(自动初始化为null),并不是创建对象new String(“hello world”);    //用new创建对象String s = new String(“hello world”);    //先用new创建对象,再创建引用s,并指向创建的对象(=具有右结合性)

Copy after login

操作符注意

==和!=用于比较基本类型的值,对象的引用是否相同

equals()比较对象的值是否相同, 但是不适用于基本类型

注意:equals默认行为是比较引用

class Value {int i;int j = 10;
}public class EqualMethod {public static void main(String[] args) {//==和!=比较基本类型的值System.out.println(47 == 47.00);    //trueInteger n1 = new Integer(47);
        Integer n2 = new Integer(47);        //==和!=比较对象的引用System.out.println(n1 == n2);        //false//equals()比较对象的值System.out.println(n1.equals(n2));    //true        
        
        Value v1 = new Value();
        Value v2 = new Value();
        v1.i = v2.i = 100;//equals()默认比较引用,这里v1,v2都为类Value的对象的引用System.out.println(v1.equals(v2));    //false    }

}

Copy after login

逻辑操作符(&&, ||, !) 产生一个布尔值,存在短路现象

按位操作符(&, |, ~, ^) 不存在短路现象

移位操作符:(<<, >>, >>>):左移<<时低位补0;有符号右移>>时,若符号为正则高位补0,为负则高位补1;无符号右移>>>时,无论正负高位补1(byte和short类型进行无符号右移时,先会被转换为int型, 再右移,然后截断赋值给原来类型)

直接常量

long: L, l(后缀)

float:F, f(后缀)

double: D, d(后缀)

十六进制: 0X, 0x(前缀)

八进制: 0(前缀)

long a = 1024L;float b = 40f;double c = 2048d;int d = 0x21;    //十进制33int e = 021;    //十进制17

Copy after login

Commonly used javadoc tags
##@see: other-class	Quoteother-class The generated html document will have a See Alse as a hyperlink The only entries are
##{@link package.class#member label}	Same as @see, but used for inline . generatedhtml The document will have a label as a hyperlink only to the entry
{@docRoot}	Generates a relative path to the document root directory , is used for displaying the document tree page Hyperlink

	Used to generate customized version information (version-information)
	Used to generate customized author information(author-information)
@since	Specify the earliest version of the program code used
@param parameter-name description	##parameter-name is the identifier of the method parameter list, description means it can be extended to multiple lines
##@return return-value description	return-value Describe the meaning of the return valuedescriptionIndicates that multiple lines can be continued
@throws fully-qualified-class-name description	fully-qualified -class-name gives an exception class name defined elsewhere ( cannot be ambiguous), description means it can Continue multiple lines
@Deprecated	Old features that users are advised not to use

The above is the detailed content of Examples of knowledge points in java. For more information, please follow other related articles on the PHP Chinese website!