千鋒逆戰班，包裝類和String類習題

在千鋒學習的第21天
不積跬步無以至千里，不積小流無以成江河！加油
今天我學習了包裝類和String類
下面是String類以及包裝類的一些習題

代碼爲：

package ques7;

import java.util.Scanner;

public class Test7 {

	public static void main(String[] args) {
		
		Scanner input = new Scanner(System.in);
		
		System.out.println("請輸入數字：");
		String str = input.next();
		
		//方法一
		int i1 = Integer.parseInt(str);
		System.out.println(i1);
		
		//方法二
		
		Integer i2 = new Integer(str);
		int i3 = i2.intValue();
		System.out.println(i3);
		
		Integer i4 = Integer.valueOf(str);
		//int i5 = i4.intValue();
		System.out.println(i4);
	}

}

8.
答案爲：ABC

package ques8;


public class TestStudent{
	public static void main(String[] args){
		Student stu1 = new Student( "tom" , 18);
		System.out.println(stu1 + " " + 100);
		System.out.println(100 + " " + stu1);
		//System.out.println(stu1 + 100 + " " );
		System.out.println(" " + 100 +stu1);
	}
}
class Student{
	private int age;
	private String name;
	public Student(){}
	public Student(String name, int age){
		this.name = name;
		this.age = age;
	}
	public String toString(){
		return name +" "+ age;
	}
}

package ques11;

public class Test11 {

	public static void main(String[] args) {
		String email = "[email protected]";
		
		System.out.println(email.substring(0,7));
	}

}

package quse12;

public class Test12 {

	public static void main(String[] args) {
		String email = "[email protected]";
		int a1 = email.indexOf("@");
		int a2 = email.indexOf(".");
		if(a1 != -1 && a2 != -1&& a1 < a2){
			System.out.println("合格的郵箱");
			
		}else{
		System.out.println("不合格");
		}
	}

}

package ques13;
import java.util.UUID;

public class Test13 {

	public static void main(String[] args) {
		
		String str = UUID.randomUUID().toString();
		
		String str1 = str.replace("-", "");
		System.out.println(str1);
		
	}

}

package ques14;


import java.util.Random;
public class Test14 {

	public static void main(String[] args) {
		Random random = new Random();
		String str1 = "ABCDEFGHijklmn1234567";
		
		StringBuilder str3 = new StringBuilder();
		int a;
		for(int i=0; i< 4;i++){
			a = random.nextInt(str1.length());
			str3.append(str1.charAt(a));
		}
		
			

		System.out.println(str3);
	}

}

package ques15;

import java.util.Scanner;

public class Test15 {

	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		System.out.println("請輸入一串數字：");
		String str = input.next();
		
		
		int[] arr = new int[10]; //這個數組下標0-9正好對應了每個數次出現次數的存放位置
		for(int i=0;i< str.length();i++){//先循環接受的字符串
			char c = str.charAt(i);//然後將得到的下標經過charAt方法轉換成字符
			for(int j=0;j< arr.length;j++){//然後和整數數組下標挨個對應
				if(c-48 == j){ //因爲0-9字符在ASCLL裏面是48-57
					arr[j]++;   
				}
			}
			
		}
		
		for(int i=0;i< arr.length;i++){
			System.out.println(i+"出現了"+arr[i]);
		}

	}