1，String类

/*
统计一个String类对象字符串，大写字母，小写字母，非字母出现的次数
 */
public class Test2 {
    public static void main(String[] args){
//        //方法一
//        String s = "abDJD, slkSDH,?.DK";
//        int countL = 0;
//        int countD = 0;
//        int countF = 0;
//        for(int i = 0;i<s.length();i++){
//            char c = s.charAt(i);
//            if(c>='a'&&c<='z'){
//                countL++;
//            }else if(c>='A'&&c<='Z'){
//                countD++;
//            }else{
//                countF++;
//            }
//        }
//        System.out.printf("小写字母出现的次数%d\t",countL);
//        System.out.printf("大写字母出现的次数%d\t",countD);
//        System.out.printf("非字母出现的次数%d\t",countF);
//        System.out.println("-----------------------");

        //方法二
        String str1 = "a、b、c、d、e、f、g、h、i、j、k、l、m、n、o、p、q、r、s、t、u、v、w、x、y、z";
        String str2 = "A、B、C、D、E、F、G、H、I、J、K、L、M、N、O、P、Q、R、S、T、U、V、W、X、Y、Z";
        String s = "abDJD, slkSDH,?.DK";
        int countL = 0;
        int countD = 0;
        int countF = 0;
        for(int i = 0;i<s.length();i++){
            char c = s.charAt(i);
            if(str1.indexOf(c)!=-1){
                countL++;
            }else if(str2.indexOf(c)!=-1){
                countD++;
            }else{
                countF++;
            }
        }
        System.out.printf("小写字母出现的次数%d\t",countL);
        System.out.printf("大写字母出现的次数%d\t",countD);
        System.out.printf("非字母出现的次数%d\t",countF);
    }
}

/*
    统一一个字符串在另一个字符串中出现的次数
*/

public class TestString4
{
    public static void main(String[] args)
    {
        String str1 = "abcasdabcabc";
        String str2 = "abc";
        int index = -1;
        int cnt = 0;

        index = str1.indexOf(str2);
        while (-1 != index)
        {
            ++cnt;
            index = str1.indexOf(str2, index+str2.length());
        }
        System.out.printf("%d\n", cnt);
    }
}

StringBuffer

 

 

 toString

 

 

public class TestToString {
    public static void main(String[] args){
        point p = new point(3,4);
        System.out.println(p);
    }
}
class point{
    int i,j;
    point(int i,int j){
        this.i = i;
        this.j = j;
    }
}

 

运行结果

 

 

public class TestToString {
    public static void main(String[] args){
        point p = new point(3,4);
        System.out.println(p);//默认System.out.println(p.toString)
    }
}
class point{
    int i,j;
    point(int i,int j){
        this.i = i;
        this.j = j;
    }
    public String toString(){//重写父类的方法
        return "["+i+","+j+"]";
    }
}