import java.util.Scanner;

public class Rank1 {
    public static void main(String[]args){
        /*Scanner in = new Scanner(System.in);
        System.out.println("请输入一行1-9的数字,以逗号分割,以回车结束!");
        String s = in.nextLine();
        int arr[] = {Integer.parseInt(s)};
        */
        int arr[] = {1,2,3,4};
        int i,j,k,temp=0;
        int count = 0;
        for(i = 0;i < arr.length;i++){
            int bai = 100*arr[i];
            for(j = 0;j<arr.length;j++){
                int shi = 10*arr[j];
                for(k = 0;k<arr.length;k++){
                    int ge = arr[k];
                    temp = bai+shi+ge;
                    count++;
                    if(count%8 == 0){
                        System.out.print(temp+" ");
                        System.out.println();
                    }else{
                        System.out.print(temp+" ");
                    }
                }
            }
        }
        System.out.println();
        System.out.println("一个可以组成"+count+"个三位数!");
    }
}

public class Rank {
    private char[] rank;
    private boolean[] vist;
    private char[] c;
    private int size;
    private long kind;
    
    public Rank(char[] c,int size){
        rank = new char[size];
        vist = new boolean[c.length];
        this.c = c;
        this.size = size;
        kind = 0;
    }
    public void showAllRank() {
        kind = 0;
        for (int i = 0; i < c.length; i++) {
            vist[i] = false;
        }
        dfs(0);
        System.out.println("kind:"+kind);
    }
    public void dfs(int level) {
        if (level == size) {
            for (int i = 0; i < size; i++) {
                System.out.print(rank[i]);
            }
            System.out.println();
            kind++;
        } else {
            for (int i = 0; i < c.length; i++) {
                if ( !vist[i]) {
                    vist[i] = true;
                    rank[level] = c[i];
                    dfs(level+1);
                    vist[i] = false; //回溯
                }
            }
        }
    }
    
}

------解决方案--------------------
rank类我给你封装好了。

new Rank(arg1,arg2)

arg1是可供选择的字符集（在你的需求里面就是你键盘输出的那几个数）
arg2是排列出的字符串多长(在你的需求里面就是几位数)



------解决方案--------------------
int[] nums=new int[]{1,2,3,4};
		int sum=0;
		for(int i=0;i<nums.length;i++){
			int a=nums[i]>0?nums[i]:nums[i<nums.length-1?i+1:-1];
			for(int k : nums){
				if(k!=a){
					for(int c:nums){
						if(c!=a&&c!=k){
							System.out.println(a+""+k+""+c);
							sum+=1;
						}
					}
				}
			}
		}
System.out.println(sum);