API(Application Programming Interface,应用程序编程接口)
下载API文档:
http://www.oracle.com/technetwork/java/javase/downloads/index.html
String类定义的变量可以用于存储字符串,同时String类提供了很多操作字符串的功能,我们可以直接使用
ArrayList代表的是集合类,集合是一种容器,与数组类似,不同的是集合的大小是不固定的。
通过创建ArrayList的对象表示得到一个集合容器,同时ArrayList提供了比数组更好用,更丰富的API(功能)给程序员使用。
String其实常被称为不可变字符串类型,它的对象在创建后不能被更改。
1.String是什么,可以做什么?
2.String是不可变字符串的原因?
package com.itheima.string;import java.sql.SQLOutput;public class StringDemo {public static void main(String[] args) {String s="我最帅";System.out.println(s);String s1 = new String();System.out.println(s1);String s2 = new String("我是中国人");System.out.println(s2);char[] chars = {'a','b','c','d'};String s3 = new String(chars);System.out.println(s3);byte [] bytes ={97,98,99,65,66,67};String s4 = new String(bytes);System.out.println(s4);}
}
String ss1 = "abc";String ss2 = "abc";System.out.println(ss1==ss2); //truechar[] chars1 = {'a','b','c'};String ss3=new String(chars1);String ss4 = new String(chars1);System.out.println(ss3==ss4);//false
1、字符串对象的特点有哪些?
s1创建了0个对象
package com.itheima.string;import java.util.Scanner;public class StringEqualsDemo4 {public static void main(String[] args) {String okName = "itheima";String okPassword = "123456";Scanner sc = new Scanner(System.in);System.out.println("登录用户名:");String name = sc.next();System.out.println("登录密码:");String password = sc.next();if(okName==name && okPassword==password){System.out.println("登录成功");}else{System.out.println("用户名或者密码错误了!");}}
}
String ss1="abcd";String ss2="ABCD";System.out.println(ss1.equals(ss2)); //falseSystem.out.println(ss1.equalsIgnoreCase(ss2));//true
1、如果是字符串比较应该使用使用什么方式进行比较,为什么?
2、开发中什么时候使用==比较数据
package com.itheima.string;public class StringAPIOtherDemo5 {public static void main(String[] args) {String name = "我爱你祖国love";System.out.println(name.length());char c = name.charAt(1);System.out.println(c);System.out.println("------遍历字符串中的每个字符------");for(int i =0;ichar ch= name.charAt(i);System.out.println(ch);}char[] chars = name.toCharArray();for(int i = 0;i < chars.length;i++){char ch =chars[i];System.out.println(ch);}String name2 = "Java是最厉害的编程语言";String rs = name.substring(0,9);System.out.println(rs);String rs1 = name2.substring(4,9);System.out.println(rs1);String rs2 = name2.substring(4);System.out.println(rs2);String name3 ="小陈是最厉害的00后,小陈棒棒哒!";String rs3 = name3.replace("小陈","小野");System.out.println(rs3);System.out.println(name3.contains("小陈")); //trueSystem.out.println(name3.contains("小孩")); //falseSystem.out.println(name3.startsWith("小陈")); //trueSystem.out.println(name3.startsWith("小陈是最厉害的")); //trueSystem.out.println(name3.startsWith("小陈最厉害")); //falseString name4 = "王宝强,贾乃亮,陈羽凡";String [] names = name4.split(",");for(int i =0;iSystem.out.println("选择了:"+names[i]);}}}
package com.itheima.string;import java.util.Random;public class StringExec8 {public static void main(String[] args) {String dates = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";String code = "";Random r =new Random();for(int i=0;i<4;i++){int indexs = r.nextInt(dates.length());char c =dates.charAt(indexs);code +=c;}System.out.println(code);}}
package com.itheima.string;import java.util.Scanner;public class StringExec7 {public static void main(String[] args) {String okLoginName = "admin";String okPassword = "itheima";Scanner sc = new Scanner(System.in);for(int i =1;i<=3;i++){System.out.println("请您输入登录用户名:");String loginName = sc.next();System.out.println("请您输入登录密码:");String password = sc.next();if(okLoginName.equals(loginName)){if(okPassword.equals(password)){System.out.println("登录成功!欢迎进入系统随意浏览~~~");break;}else{System.out.println("您的密码不正确!您还剩余"+(3-i)+"次机会登录");}}else{System.out.println("您的登录名称不正确!您还剩余"+(3-i)+"次机会登录");}}}}
package com.itheima.string;import java.util.Scanner;public class StringExec6 {public static void main(String[] args) {Scanner sc = new Scanner(System.in);System.out.println("请您输入您的手机号码:");String tel = sc.next();String before = tel.substring(0,3);String after = tel.substring(7);String s = before +"****" + after;System.out.println(s);}
}