Think in java笔记（二）

1.for (float x :f ) for循环的简易形式

Exercise for Controlling Execution

Exercise1:

package control;
//:print values from 1 to 100
public class Exercise01 {
    public static void main(String[] args) {
        for (int i = 1;i <= 100;i ++) {
            System.out.println(i);
            if (i == 99) {
                break;
            }
        }
    }
}

Exercise2:

package control;
//:random int value compares 
import java.util.*;
public class Exercise02 {
    static void condition(int x,int y) {
        if (x > y) {
            System.out.println("x is greater than y");
        }
        else if(x < y) {
            System.out.println("x is smaller than y");
        }
        else {
            System.out.println("x is equal to y");
        }
    }
    public static void main(String[] args) {
        Random r = new Random();
        for (int i = 0;i < 25;i++) {
            int x = r.nextInt(25);
            int y = r.nextInt(25);
            condition(x,y);
    }
}
}

Exercise4:

package control;

public class Exercise04 {
    static void prime_number_test(int n) {
        for (int i = 1;i <= n;i ++) {
            for (int j = 2; j < i;j ++) {
                if ((j == i - 1) & (i % j != 0)) {
                    System.out.println(i);
                }
                if (i % j == 0) {
                    break;
                }
            }
        }
    }
    
    public static void main(String[] args) {
        prime_number_test(30);
    }
}

Exercise6:

package control;
import java.util.*;
public class Exercise06 {
    static int test(int testval,int begin,int end) {
        for (int i = begin;i <= end;i++) {
            if (testval == i){
                return 1;
            }
        }
        return 0;
    }
    public static void main(String[] args) {
        Random r = new Random();
        Integer t[] = new Integer[10]; 
        for (int i = 0;i < 10;i ++) {
            t[i] = r.nextInt(47);
        }
        for (int x : t) {
            System.out.println(test(x,0,20));
        }
    }
}

Exercise9:

package control;
//:fibonacci
public class Exercise09 {
    static void Fibonacci(int num) {
        if (num == 1) {
            System.out.print(1);
        }
        else {
            System.out.print(1+","+1+","+2);
            int sum = 2;
            int i = 1;
            while(sum <= num) {
                int temp = sum;
                sum = i + sum;
                i = temp;
                System.out.print(","+sum);
            }
        }
    }
    public static void main(String[] args) {
        Fibonacci(100);
    }
}

Exercise10:

package control;
//:vampire digits
import java.util.*;
public class Exercise10 {
    
    static void vampire(int i) {
            int qian = i / 1000;
            int bai = i % 1000 / 100;
            int shi = i % 1000 % 100 /10;
            int ge = i % 1000 % 100 % 10;
            Integer[] t1 = new Integer[4];
            ArrayList<Integer> a1 = new ArrayList<Integer>();
            ArrayList<Integer> a2 = new ArrayList<Integer>();
            t1[0] = qian;
            t1[1] = bai;
            t1[2] = shi;
            t1[3] = ge;
            for (int x : t1) {
                for (int y : t1) {
                    int factor1 = x * 10 + y;
                    a1.add(factor1);
                }
            }
            for (int x : t1) {
                for (int y : t1) {
                    int factor2 = x * 10 + y;
                    a2.add(factor2);
                }
            }
            for (int x : a1) {
                for (int y : a2) {
                    if (i == x * y) {
                        System.out.println(i);
                        return;
                    }
                }
            }
            
        }
    public static void main(String[] args) {
        for (int i = 1000;i <= 9999;i ++) {
            vampire(i);
        }

    }
}