1 String类的概述
- 在实际开发中，字符串的操作是最常见的操作，没有之一。
- Java中没有内置的字符串类型，所以，Java提供了一个类String供我们使用。
- 字符串是由多个字符组成的一串字符。
- 字符串可以看成是字符序列。
2 String类的构造方法
public String(byte[] bytes){}
public String(byte[] bytes,int offset,int length){}
public String(char[] value){}
public String(char[] value,int offset,int length){}
public String(String original){}
package com.xuweiwei;
public class StringDemo {
public static void main(String[] args) {
//public String(){}
String s1 = new String();
System.out.println("s1:" + s1);
System.out.println("s1.length():" + s1.length());
System.out.println("--------------");
//public String(byte[] bytes){}
byte[] bytes = {97,98,99,100,101};
String s2 = new String(bytes);
System.out.println("s2:" + s2);
System.out.println("s2.length():" + s2.length());
System.out.println("--------------");
//public String(byte[] bytes,int offset,int length){}
byte[] bytes2 = {97,98,99,100,101};
String s3 = new String(bytes2,2,2);
System.out.println("s3:" + s3);
System.out.println("s3.length():" + s3.length());
System.out.println("--------------");
//public String(char[] value){}
char[] chs = {'a','b','c','d'};
String s4 = new String(chs);
System.out.println("s4:" + s4);
System.out.println("s4.length():" + s4.length());
System.out.println("--------------");
//public String(String value)
String s5 = new String("abvc");
System.out.println("s5:" + s5);
System.out.println("s5.length():" + s5.length());
System.out.println("--------------");
}
}
3 String的特点
4 String类的判断功能
public boolean equals(String str)
public boolean equalsIgnoreCase(String str)
public boolean contains(String str)
public boolean startsWith(String str)
public boolean endsWith(String str)
package com.xuweiwei;
import java.util.Scanner;
public class StringDemo2 {
public static void main(String[] args) {
String username = "admin";
String passwrod = "admin";
Scanner input = new Scanner(System.in);
for (int x = 0; x < 3; x++) {
System.out.print("请输入用户名:");
String name = input.nextLine();
System.out.print("请输入密码：");
String pwd = input.nextLine();
if (username.equals(name) && passwrod.equals(pwd)) {
System.out.println("恭喜你，登录成功");
break;
} else {
if ((2 - x) == 0) {
System.out.println("o(╥﹏╥)o，您的账号被锁定，请和管理员联系");
break;
}
System.out.println("登录失败，你还有" + (2 - x) + "此机会");
}
}
}
}
5 String类的获取功能
public char charAt(int index)
public int indexOf(int ch)
public int indexOf(String str)
- 示例：从指定的索引开始，返回此字符在指定的字符串中出现的第一次索引位置
public int indexOf(int ch,int offset)
- 示例：从指定的索引开始，返回此字符串在指定的字符串中出现的第一次索引的位置
public int indexOf(String str,int offset)
public String substring(int start)
public String substring(int start,int end)
package com.xuweiwei;
public class StringDemo3 {
public static void main(String[] args) {
String str = "abc";
for(int x = 0;x<str.length();x++){
char ch = str.charAt(x);
System.out.println(ch);
}
}
}
package com.xuweiwei;
public class StringDemo4 {
public static void main(String[] args) {
String str = "hello123WorLd";
int bigCount = 0;
int smallCount = 0;
int numberCount = 0;
for (int x = 0; x < str.length(); x++) {
char ch = str.charAt(x);
if(ch >= '0' && ch <= '9'){
numberCount ++;
}
if(ch >= 'a' && ch <='z' ){
smallCount++;
}
if(ch >='A' && ch<='Z'){
bigCount++;
}
}
System.out.println("大写字符的个数是："+bigCount);
System.out.println("小写字符的个数是："+smallCount);
System.out.println("数字字符的个数是："+numberCount);
}
}
6 String类的转换功能
public char[] toCharArray()
public static String valueOf(char[] chs)
public static String valueOf(int i)
public String toLowerCase()
public String toUpperCase()
public String concat(String str)
7 String类的其他功能
public String replace(char old,char new)
public replace(String old,String new)
public int compareTo(String str)
public int compareToIgnoreCase(String str)