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java中的biconsumer(Java中的for循环)

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JAVA中的public classa是什么意思?为什么只能有一个?谢谢

public class是公共类的意思,public 是访问修饰符.为什么只有一个,java规定,一个类文件,public 修类的class只有一个,并且类名必须和你新建的这个类文件名一样,所以一个类文件中可以有多个类,但由public修饰的类只能有一个。

扩展资料:

Java具有简单性、面向对象、分布式、健壮性、安全性、平台独立与可移植性、多线程、动态性等特点  。Java可以编写桌面应用程序、Web应用程序、分布式系统和嵌入式系统应用程序等。

编程工具

Eclipse:一个开放源代码的、基于Java的可扩展开发平台 。

NetBeans:开放源码的Java集成开发环境,适用于各种客户机和Web应用。

IntelliJ IDEA:在代码自动提示、代码分析等方面的具有很好的功能。

MyEclipse:由Genuitec公司开发的一款商业化软件,是应用比较广泛的Java应用程序集成开发环境 。

EditPlus:如果正确配置Java的编译器“Javac”以及解释器“Java”后,可直接使用EditPlus编译执行Java程序 。

工作原理:

由四方面组成:

(1)Java编程语言

(2)Java类文件格式

(3)Java虚拟机

(4)Java应用程序接口

参考资料:百度百科:java

菜鸟网:Java基础语法

Java从入门到精通(第3版):清华大学出版社:豆瓣

JAVA语言中,什么叫方法过载?

你好,java里“方法过载”也就是“方法重载”,表示类中允许出现参数不同的同名方法,比如下面的类中的B方法就是

public

class

A{

public

void

B(){}

public

void

B(int

b){}

}

java中abstract怎么使用啊,说的详细点。举几个有代表的例子

使用abstract(抽象)修饰符,可以修饰类和方法。

1、abstract修饰类,会使这个类成为一个抽象类,这个类将不能生成对象实例,但可以做为对象变量声明的类型,也就是编译时类型,抽象类就像当于一类的半成品,需要子类继承并覆盖其中的抽象方法。

2、abstract修饰方法,会使这个方法变成抽象方法,也就是只有声明(定义)而没有实现,实现部分以";"代替。需要子类继承实现(覆盖)。

注意:有抽象方法的类一定是抽象类。但是抽象类中不一定都是抽象方法,也可以全是具体方法。

abstract修饰符在修饰类时必须放在类名前。

abstract修饰方法就是要求其子类覆盖(实现)这个方法。调用时可以以多态方式调用子类覆盖(实现)后的方法,也就是说抽象方法必须在其子类中实现,除非子类本身也是抽象类。

注意:父类是抽象类,其中有抽象方法,那么子类继承父类,并把父类中的所有抽象方法都实现(覆盖)了,子类才有创建对象的实例的能力,否则子类也必须是抽象类。抽象类中可以有构造方法,是子类在构造子类对象时需要调用的父类(抽象类)的构造方法。

举个简单的例子下面有一个抽象类:

abstract class E{

public  abstract  void  show();//public abstract 可以省略

}

然后其它类如果继承它通常为了实现它里面的方法:

class F extends E{

void show(){

//写具体实现的代码

}

}

最后再主方法里面定义一个父类引用指向子类对象,就会发生多态现象,比如 :

E e=new F();

e.show();

实际调用了子类里面的show()方法 。

扩展资料:

Java中的abstract方法和abstract类的问题:

当知道一个类的子类将不同的实现某个方法时,把该类声明为抽象类很有用,可以共用相同的父类方法,不必再定义。

抽象类和抽象方法的关系:含有抽象方法的类一定是抽象类,抽象类里不一定含有抽象方法。

抽象类存在的意义是用来被继承的。一个类继承了一个抽象类,必须实现抽象类里面所有的抽象方法,否则,此类也是抽象类。

1:用abstract修饰的类表示抽象类,抽象类位于继承树的抽象层,抽象类不能被实例化。

2:用abstract修饰的方法表示抽象方法,抽象方法没有方法体。抽象方法用来描述系统具有什么功能,但不提供具体的实现。

abstract 的规则:

1:抽象类可以没有抽象方法,但是有抽象方法的类必须定义为抽象类,如果一个子类继承一个抽象类,子类没有实现父类的所有抽象方法,那么子类也要定义为抽象类,否则的话编译会出错的。

2:抽象类没有构造方法,也没有抽象静态方法。但是可以有非抽象的构造方法。

3:抽象类不能被实例化,但是可以创建一个引用变量,类型是一个抽象类,并让它引用非抽象类的子类的一个实例。

4:不能用final 修饰符修饰。

参考资料:

百度百科--abstract

java 库里的 BiConsumer 可以强制转换成 Consumer 吗

可以直接通过参数前面加上要转行的类型的形式实现。 举例: int i =97; char c = (char)i; System.out.print(c); 输出结果:a。 备注:并不是所有的类型都可以强制转换的,所有在开发过程中要遵循对象转换规则(相关类型才可以转换)。

JAVA 中Stringbuilder类的方法

StringBuilderpublic StringBuilder() 构造一个其中不带字符的字符串生成器,初始容量为 16 个字符。 StringBuilderpublic StringBuilder(int capacity) 构造一个其中不带字符的字符串生成器,初始容量由 capacity 参数指定。 参数: capacity - 初始容量。 抛出: NegativeArraySizeException - 如果 capacity 参数小于 0。StringBuilderpublic StringBuilder(String str) 构造一个字符串生成器,并初始化为指定的字符串内容。该字符串生成器的初始容量为 16 加上字符串参数的长度。 参数: str - 缓冲区的初始内容。 抛出: NullPointerException - 如果 str 为 nullStringBuilderpublic StringBuilder(CharSequence seq) 构造一个字符串生成器,包含与指定的 CharSequence 相同的字符。该字符串生成器的初始容量为 16 加上 CharSequence 参数的长度。 参数: seq - 要复制的序列。 抛出: NullPointerException - 如果 seq 为 null方法详细信息appendpublic StringBuilder append(Object obj) Appends the string representation of the Object argument. The argument is converted to a string as if by the method String.valueOf, and the characters of that string are then appended to this sequence. 参数: obj - an Object. 返回: a reference to this object. 另请参见: String.valueOf(java.lang.Object), append(java.lang.String)/ddappendpublic StringBuilder append(String str) Appends the specified string to this character sequence. The characters of the String argument are appended, in order, increasing the length of this sequence by the length of the argument. If str is null, then the four characters "null" are appended. Let n be the length of this character sequence just prior to execution of the append method. Then the character at index k in the new character sequence is equal to the character at index k in the old character sequence, if k is less than n; otherwise, it is equal to the character at index k-n in the argument str. 参数: str - a string. 返回: a reference to this object./ddappendpublic StringBuilder append(StringBuffer sb) 将指定的 StringBuffer 添加到此序列。 按顺序将 StringBuffer 参数中的字符添加到该序列中,使该序列在长度上增加该参数的长度。如果 sb 为 null,则向该序列中添加 4 个 "null" 字符。 在执行 append 方法前,让此字符序列的长度为 n。如果 k 小于 n,则新字符序列中索引 k 处的字符等于原有序列中索引 k 处的字符;否则它等于参数 sb 中索引 k-n 处的字符。 参数: sb - 要添加的 StringBuffer。 返回: 此对象的一个引用。/ddappendpublic StringBuilder append(CharSequence s) 从接口 Appendable 复制的描述 向此 Appendable 添加指定的字符序列。 有时可能没有添加整个序列,这取决于使用哪个类来实现字符序列 csq。例如,如果 csq 是 CharBuffer 的一个实例,则通过缓冲区的位置和限制来定义要添加的子序列。 指定者: 接口 Appendable 中的 append参数: s - 要添加的字符串序列。如果 csq 为 null,则向该 Appendable 添加四个字符 "null"。 返回: 此 Appendable 的引用 抛出: IndexOutOfBoundsException/ddappendpublic StringBuilder append(CharSequence s, int start, int end) Appends a subsequence of the specified CharSequence to this sequence. Characters of the argument s, starting at index start, are appended, in order, to the contents of this sequence up to the (exclusive) index end. The length of this sequence is increased by the value of end - start. Let n be the length of this character sequence just prior to execution of the append method. Then the character at index k in this character sequence becomes equal to the character at index k in this sequence, if k is less than n; otherwise, it is equal to the character at index k+start-n in the argument s. If s is null, then this method appends characters as if the s parameter was a sequence containing the four characters "null". 指定者: 接口 Appendable 中的 append参数: s - the sequence to append. start - the starting index of the subsequence to be appended. end - the end index of the subsequence to be appended. 返回: a reference to this object. 抛出: IndexOutOfBoundsException - if start or end are negative, or start is greater than end or end is greater than s.length()/ddappendpublic StringBuilder append(char[] str) Appends the string representation of the char array argument to this sequence. The characters of the array argument are appended, in order, to the contents of this sequence. The length of this sequence increases by the length of the argument. The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(char[]) and the characters of that string were then appended to this character sequence. 参数: str - the characters to be appended. 返回: a reference to this object./ddappendpublic StringBuilder append(char[] str, int offset, int len) Appends the string representation of a subarray of the char array argument to this sequence. Characters of the char array str, starting at index offset, are appended, in order, to the contents of this sequence. The length of this sequence increases by the value of len. The overall effect is exactly as if the arguments were converted to a string by the method String.valueOf(char[],int,int) and the characters of that string were then appended to this character sequence. 参数: str - the characters to be appended. offset - the index of the first char to append. len - the number of chars to append. 返回: a reference to this object./ddappendpublic StringBuilder append(boolean b) Appends the string representation of the boolean argument to the sequence. The argument is converted to a string as if by the method String.valueOf, and the characters of that string are then appended to this sequence. 参数: b - a boolean. 返回: a reference to this object. 另请参见: String.valueOf(boolean), append(java.lang.String)/ddappendpublic StringBuilder append(char c) Appends the string representation of the char argument to this sequence. The argument is appended to the contents of this sequence. The length of this sequence increases by 1. The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(char) and the character in that string were then appended to this character sequence. 指定者: 接口 Appendable 中的 append参数: c - a char. 返回: a reference to this object./ddappendpublic StringBuilder append(int i) Appends the string representation of the int argument to this sequence. The argument is converted to a string as if by the method String.valueOf, and the characters of that string are then appended to this sequence. 参数: i - an int. 返回: a reference to this object. 另请参见: String.valueOf(int), append(java.lang.String)/ddappendpublic StringBuilder append(long lng) Appends the string representation of the long argument to this sequence. The argument is converted to a string as if by the method String.valueOf, and the characters of that string are then appended to this sequence. 参数: lng - a long. 返回: a reference to this object. 另请参见: String.valueOf(long), append(java.lang.String)/ddappendpublic StringBuilder append(float f) Appends the string representation of the float argument to this sequence. The argument is converted to a string as if by the method String.valueOf, and the characters of that string are then appended to this string sequence. 参数: f - a float. 返回: a reference to this object. 另请参见: String.valueOf(float), append(java.lang.String)/ddappendpublic StringBuilder append(double d) Appends the string representation of the double argument to this sequence. The argument is converted to a string as if by the method String.valueOf, and the characters of that string are then appended to this sequence. 参数: d - a double. 返回: a reference to this object. 另请参见: String.valueOf(double), append(java.lang.String)/ddappendCodePointpublic StringBuilder appendCodePoint(int codePoint) Appends the string representation of the codePoint argument to this sequence. The argument is appended to the contents of this sequence. The length of this sequence increases by Character.charCount(codePoint). The overall effect is exactly as if the argument were converted to a char array by the method Character.toChars(int) and the character in that array were then appended to this character sequence. 参数: codePoint - a Unicode code point 返回: a reference to this object. 从以下版本开始: 1.5 /dddeletepublic StringBuilder delete(int start, int end) Removes the characters in a substring of this sequence. The substring begins at the specified start and extends to the character at index end - 1 or to the end of the sequence if no such character exists. If start is equal to end, no changes are made. 参数: start - The beginning index, inclusive. end - The ending index, exclusive. 返回: This object. 抛出: StringIndexOutOfBoundsException - if start is negative, greater than length(), or greater than end./dd/dd/dl/dl

java.util.function.biconsumer 用什么jar包

import java.util.*;util代表工具类,包含一些日期转换、字符串处理、获取编译环境信息。

假如没这句话的话,如果你要用java.util包中的类Scanner的话就需要这样使用 java.util.Scanner sc = new java.util.Scanner();

而import java.util.*;代表导入了java.util包中的所有类,,这样的话使用 Scanner就没那么麻烦了Scanner sc = new Scanner();