[PHP知识库]Java 字符串

API

import java.util.scanner 

public class ScannerDemo{
    public static void main(String[] args){
        //创建对象
        Scanner sc = new Scanner(System.in);

        //接收数据
        System.out.println("请输入一个字符串数据")；
        String line = sc.nextLine();

        //输出结果
        System.out.println("你输入的数据是："+line);
    }
}

String

String构造方法

import java.util.scanner 

public class StringDemo{
    public static void main(String[] args){

        String s1 = new String();
        System.out.println("s1:" + s1);

        char[] chs = {'a','b','c'};
        String s2 = new String(chs);
        System.out.println("s2:" + s2);

        byte[] bys = {97,98,99};
        String s3 = new String(bys);
        System.out.println("s3:" + s3); 

        String s4 = "abc"
        System.out.println("s4:" + s4);         
        //推荐使用直接赋值的方式
    }
}

String 字符串的比较

使用==做比较

• 基本类型：比较的是数据值是否相同
• 引用类型：比较的是地址值是否相同

使用equals()做比较

• 基本类型：比较的是内容是否相同
• 引用类型/；比较的是内容是否相同

import java.util.scanner 

public class StringDemo02{
    public static void main(String[] args){

        char[] chs = {'a','b','c'};
        String s1 = new String(chs);
        String s2 = new String(chs);

        String s3 = "abc";
        String s4 = "abc";

        System.out.println(s1==s2); 
        System.out.println(s1==s3); 
        System.out.println(s3==s4); 

        System.out.println(s1.equals(s2)); 
        System.out.println(s1.equals(s3)); 
        System.out.println(s3.equals(s4)); 

    }
}

String 字符串的遍历

public class StringDemo03{
    public static void main (String[] args){
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入一个字符串")
        String line = sc.nextLine();

       for(int i=0; i<line.length(); i++){
            System.out.println(line.charAt(i)); 
        }
    }
}

String 字符次数统计

public class StringDemo04{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入一个字符串：")
        String line = sc.nextLine();

        int bigCount = 0;
        int smallCount = 0;
        int numberCount = 0;   

        for(int i=0; i<line.length(); i++){
            char ch = line.charAt(i);

            if(ch>='A' && ch<='Z'){
                bigCount++;
            }else if(ch>='a' && ch<='z'){
                smallCount++;
            }else if(ch>='0' && ch<='9'){
                numberCount++;
            }
        }     

        System.out.println("大写字母：" + bigCount + "个");
        System.out.println("小写字母：" + smallCount + "个");
        System.out.println("数字：" + numberCount + "个");

    }
}

String 字符串的拼接

public class StringDemo05{
    public static void main(String[] args){
        int[] arr = {1,2,3};
        String s = ArrayToString(arr);

        System.out.println("s: " + s);
    }

    public static String ArrayToString(int[] arr){
        String s = "";

        s + = "[";

        for(int i=0, i<arr.length; i++){
            if(i==arr.length-1){
                s + = arr[i];
            }else if{
                s + = arr[i];
                s + = ", ";
            }
        }

        s + = "]";

        return s; 
    }
}

String 字符串的反转

public class StringDemo06{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入一个字符串： ");
        String line = sc.nextLine();

        String s = reverse(line);

        System.out.println("s: " + s);

    }

    public static String reverse(String s){
        String ss = "";
        for(int i = s.length()-1; i>=0; i--){
            ss += s.charAt(i);
        }

        return ss; 

    }

}

StringBuilder

StringBuilder 构造方法

public class StringDemo06{
    public static void main(String[] args){
        StringBuilder sb = new StringBuilder();
        System.out.println("sb: " + sb);  

        StringBuilder sb2 = new StringBuilder("hello");
        System.out.println("sb2: " + sb2);

    }
}

StringBuilder 添加和反转方法

public class StringDemo06{
    public static void main(String[] args){
        StringBuilder sb = new StringBuilder();
        StringBuilder sb2 = sb.append("hello");
        StringBuilder sb3 = sb2.reverse();

        System.out.println("sb: " + sb);   
        System.out.println("sb2: " + sb2);  
        System.out.println("sb3: " + sb3); 

    }
}

public class StringDemo06{
    public static void main(String[] args){
        StringBuilder sb = new StringBuilder();
        
        sb.append("hello").append("world");
        sb.reverse();

        System.out.println("sb: " + sb);  
 
    }
}

StringBuilder 和 String 相互转换

public class StringDemo06{
    public static void main(String[] args){
        StringBuilder sb = new StringBuilder();
        sb.append("hello");

        String s = sb.toString();  
        System.out.println("s: " + s);

        
        String s = "hello";
        StringBuilder sb = new StringBuilder(s);
        System.out.println("sb: " + sb);

    }
}

StringBuilder 字符串的拼接

public class StringDemo05{
    public static void main(String[] args){
        int[] arr = {1,2,3};
        String s = arrayToString(arr);

        System.out.println("s: " + s);
    }

    public static String arrayToString(int[] arr){
        StringBuilder sb = new StringBuilder();

        sb.append("[");

        for(int i=0, i<arr.length; i++){
            if(i==arr.length-1){
                sb.append(arr[i]);
            }else if{
                sb.append(arr[i]).append("' ");

            }
        }

        sb.append("]");

        String s = sb.toString();

        return s;
    }
}

StringBuilder 字符串的反转

public class StringDemo06{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入一个字符串： ");
        String line = sc.nextLine();

        String s = reverse(line);

        System.out.println("s: " + s);

    }

    public static String reverse(String s){
        //StringBuilder sb = new StringBuilder(s);
        //sb.reverse()
        //String ss = sb.toString();
        //return ss;

        return new StringBuilder(s).reverse().toString();
 

    }

}