一、javaSE （十二）scanner的使用、 String类的概述和使用

1: scanner的使用(了解）

         (1)在JDK5以后出现的用于键盘录入数据的类

         (2)构造方法

                   A:讲解了System.in这个东西。

                            它其实是标谁的输入流,对应于键盘录入

                   B:构造方法

                            Inputstream is=System.in;

                            Scanner (Inputstream is)

                   c:常用的格式

                            Scanner sc= new Scanner(System. in);

         (3)基本方法格式

                   A: hasnextxxx()判断是否是某种类型的

                   B: nextxxx()返回某种类型的元素

         (4)要掌握的两个方法

                   A: public int nextint ()

                   B: public String nextline()

         (5)需要注意的小问题

                   A:同一个 Scanner对象,先获取数值,再获取字符串会出现一个小问题。

                   B:解决方案:

                   a:重新定义一个 Scanner对象

                   b:把所有的数据都用字符患获取,然后再进行相应的转换

2: String类的概述和使用(掌握)

         (1)多个字符组成的一串数据

                   其实它可以和字符数组进行相互转换

         (2)构造方法

                   A: public String()

                   B: public String(byte [] bytes)

                   C: public String(byte[] bytes, int offset, int length)

                   D: public String(char [] value)

                   E: public String(char[] valuer,int offset,int count)

                   F: public String(String, original)

                  

                   下面的这一个虽然不是构造方法,但是结果也是一个字符串对象

                   G: String s ="hello";

         (3)字符患的特点

                   A:字符患一息被赋值,就不能改变

                   注意:这里指的是字符串的内容不能改变,而不是引用不能改变。

                   B:字面值作为字符患对象和通过构造方法创建对象的不同

                   String s= new String("he11o");和 String s="he11o"的区别?

         (4)字符患的面试题(看程序写结果)

                   A:==和equa1()

                            String s1 new String("hello");

                            String s2= new String("hello);

                            System. out. println(s1==s2);//fa1se

                            System. out. println(sl equals(s2));//true

                            String s3= new String("hello");

                            String s4 ="hello";

                            System. out. printin(s3==$4);//false

                            System. out. println(s3 equals(s4));//true

                            String s5 ="hello";

                            String s6="hello";

                            System. out. printin(s5 ==s6);//true

                            System. out. println (s5equals(s6));//true

                   B:字符患的拼接

                            String s1 ="hello";

                            String s2 ="world";

                            String s3 ="helloworld";

                            System. out. printin(s3 == s1+s2);// false

                            System. out. println(s3 equals((s1+s2)));//true

                            system,out. print1n(s3=="he11o"+" world");//true

                            System. out. println(s3 equals("hello"+"world"));//true

         (5)字符串的功能(自已补齐方法)

                   A:判断功能

                            boolean equals(Object obj)

                            boolean equalsignorecase(String str)

                            boolean contains(String str)

                            boolean startswith (String str)

                            boolean endswith(String str)

                            boolean isempty()

                   B:获取功能

                            int length()

                            char charat (int index)

                            int indexOf(int ch)

                            int indexof(String str)

                            int indexOf(int ch, int fromIndex)

                            int indexOf(String strr int fromIndex)

                            String substring (int start)

                            String substring (int start, int end)

                   c:转换功能

                            byte[] getBytes ()

                            char[] tocharArray ()

                            static String valueOf(char[] chs)

                            static String valueOf(int i)

                            String toLowerCase()

                            String toUpperCase()

                            String concat(String str)

                   D:其他功能

                            a:替换功能

                                     String replace(char old, char new)

                                     String replace(String old, String new)

                            b:去空格功能

                                     String trim()

                            c:按字典比较功能

                            int compareTo(String str)

                            int compareToIgnoreCase(String str)