Thing in java 第四章，控制执行流程，练习题答案

/**
 * Created by Sandy.Liu on 2018/7/19.
 * Thinking in java, version 4, chapter 4, practice 1
 * Write a program to print from 1 to 100
 */
public class Chap4Prac1Printfrom1To100 {
    public static void main(String[] args){
        for(int i=1;i<=100;i++)
            P.print(i+" ");
    }
}

/**
 * Created by Sandy.Liu on 2018/7/19.
 * Thinking in java, chapter 4, practice 2
 * Write a program which generating 25 random int numbers. Use if-else statement to classify it as
 * greater than, less than or equal to a second randomly generated value.
 */
import java.util.*;
public class Chap4Prac2Generate25int {
    public static void main(String[] args){
        Random ran1 = new Random();
        Random ran2 = new Random();
        P.print("ran1: "+ran1);
        P.print("ran2: "+ran2);
        for(int i=0;i<25;i++){
            int x = ran1.nextInt();
            int y = ran2.nextInt();
            if(x>y)
                P.print(x+">"+y);
            else if(x<y)
                P.print(x+"<"+y);
            else
                P.print(x+"="+y);
        }

    }

}

import java.util.Random;

/**
 * Created by Sandy.Liu on 2018/7/19.
 * Thinking in java, version 4, chapter 4, practice 3
 */
import java.util.*;
public class Chap4Prac3 {
    public static void main(String[] args){
        Random ran3 = new Random();
        Random ran4 = new Random();
        while(true){
            int x = ran3.nextInt(10);
            int y = ran4.nextInt(10);
            if(x>y)
                P.print(x+">"+y);
            else if(x<y)
                P.print(x+"<"+y);
            else
                P.print(x+"="+y);

}}}

/**
 * Created by Sandy.Liu on 2018/7/19.
 * Thinking in java, version 4, chapter 4, practice 4
 * Write a program using two nested for loops and the modules operator(%) to detect and print
 * prime numbers
 */
public class Chap4Prac4For {
    public static void main(String[] args){
        for(int i = 1;i<100;i++){
            int factor = 0;
            for(int j=1;j<=i;j++){
                if(i%j==0)
                    factor++;
            }
            if(factor<=2)
                P.print(i);
        }
    }
}

/**
 * Created by Sandy.Liu on 2018/7/19.
 * Thinking in java, version 4, chapter 4, practice 5
 */
public class Chap4Prac5 {
    static void binaryPrint(int q){
        if(q==0) P.print(0);
        else{
            int nlz = Integer.numberOfLeadingZeros(q);
            q<<=nlz;
            for(int p=0;p<32-nlz;p++){
                int n = (Integer.numberOfLeadingZeros(q)==0)?1:0;
                System.out.println(n);
                q<<=1;
            }
        }
        P.print("");

    }
    public static void main(String[] args){
        int i=1+4+16+64;
        int j = 2+8+32+128;
        int k = 0x100;
        int m = 0;
        P.print("Using Integer.toBinaryString(): ");
        P.print("i =  "+Integer.toBinaryString(i));
        P.print("j = "+Integer.toBinaryString(j));
        P.print("k = "+Integer.toBinaryString(k));
        P.print("m= "+Integer.toBinaryString(m));
        P.print("i & j = "+(i&j)+"="+Integer.toBinaryString(i&j));
        P.print("i | j = "+(i|j)+"="+Integer.toBinaryString(i|j));
        P.print("i ^ j = "+(i^j)+"="+Integer.toBinaryString(i^j));
        P.print("~i = "+Integer.toBinaryString(~i));
        P.print("~j = "+Integer.toBinaryString(~j));
        P.print("Using binaryPrint():");
        P.print("i = "+i+" = ");
        System.out.print(i);
        P.print("j = "+j+" = ");
        System.out.print(j);
        P.print("k = " + k + " = ");
        System.out.print(k);
        P.print("m = " + m + " = ");
        System.out.print(m);
        P.print("i & j = " + (i & j) + " = ");
        System.out.print(i & j);
        P.print("i | j = " + (i | j) + " = ");
        System.out.print(i | j);
        P.print("i ^ j = " + (i ^ j) + " = ");
        System.out.print(i ^ j);
        P.print("~i = " + ~i + " = ");
        System.out.print(~i);
        P.print("~j = " + ~j + " = ");
        System.out.print(~j);
    }
}

/**
 * Created by Sandy.Liu on 2018/7/22.
 * Thinking in java, version 4, chapter 4, practice 6
 * Modify method test(), make them accept two other parameters begin and end, check if
 * testval is between begin and end.
 */
public class Chap4Prac6 {
    static int test(int testval, int begin, int end){
        if (end<begin)
            P.print("end cannot be smaller than begin");
        else if((testval <=end) &(testval>=begin))
            return +1;
        else if((testval<begin)||(testval>end))
            return -1;
        else
            P.print("exceptional case");
            return 13;
    }
    public static void main(String[] args){
        test(10, 5,4);//begin<end
        P.print("case2: "+test(5,4,10));//begin<testval<end
        P.print("case3: "+test(1,4,10));//testval<begin
       P.print( "case4: "+test(5,5,6));//testval=begin
        P.print("case5: "+test(5,1,5));//testval=end
        P.print("case6: "+test(10,1,5));//testval>end
    }
}

/**
 * Created by Sandy.Liu on 2018/7/22.
 * Thinking in java, version 4, chapter 4, practice 7
 * Modify excise 1, use break to make program exists at value 99
 */
public class Chap4Prac7{
    static void test(int x){
        for(int i=0;i<=x;i++){
            if(i==99)
                break;
            P.print(i);
        }
    }
    static void test1(int x){
        for(int i=0;i<=x;i++){
            if(i==99)
                return;
            P.print(i);
        }
    }
    public static void main(String[] args) {
        test(100);
        test1(1000);
    }
}

/**
 * Created by Sandy.Liu on 2018/7/23.
 * Thinking in java, version 4, chapter 4, practice 8
 * Create a switch statement that prints a message for each case, and put the switch inside a for loop
 * to try each case. Put a break after each case and test it. And then remove the breaks and test again.
 */
public class Chap4Prac8Switch {
    public static void main(String[] args){
        for(int i = 0;i<100;i++){
            switch (i){
                case 0: P.print("zero");break;
                case 1: P.print("one");break;
                case 2: P.print("two");break;
                case 3: P.print("three");break;
                default: P.print(i+"more than three");
            }
        }
    }
}

import java.lang.reflect.Array;
import java.util.ArrayList;

/**
 * Created by Sandy.Liu on 2018/7/23.
 * Thinking in java, version 4, chapter 4, practice 9
 * A Fibonacci sequence is the sequence of numbers 1, 1, 2, 3, 5, 8, 13, 21, 34, and so on,
 * each number (from the third one ) is the sum of the previous two numbers.
 * Create a method that takes a integer as parameter,and display all Fibonacci numbers starting
 * from the beginning to the gave parameter. e.g., if you run javaFibonacci 5 (where Fibonacci
 * is the name of the class) the output will be 1, 1, 2, 3, 5.
 */
public class Chap4Prac9Fibonacci {
    static void gFib(int i) {
        if (i <= 0)
            P.print("please input a number bigger than 0");
        int[] a = new int[i];
        if (i <= 2) {
            for (int k = 0; k < i; k++)
                a[k] = 1;
        } else {
            a[0] = 1;
            a[1] = 1;
            for (int j = 2; j < i; j++)
                a[j] = a[j - 2] + a[j - 1];
        }
        for (int m = 0; m < i; m++){
            System.out.print(a[m]);
        }
        P.print(" ");
    }

    public static void main(String[] args){
        gFib(0);
        gFib(1);
        gFib(2);
        gFib(5);
        }

}

/**
 * Created by Sandy.Liu on 2018/7/25.
 * Thinking in java, version 4, chapter 4, practice 10
 * A vampire number has an even number of digits and is formed by multiplying a pair of numbers
 * containing half the number of digits of the result.
 * The digits are taken from the original number in any order. Pairs of railing zeros are not
 * allowed. Examples include:1260 = 21 * 60, 1827 = 21 * 87,
 * 2187 = 27  * 81.
 * Write a program that finds all the 4-digit vampire numbers.
 */
public class Chap4Prac10VaimpireNumber {
    static int a(int i) {
        return i / 1000;
    }

    static int b(int i) {
        return (i % 1000) / 100;
    }

    static int c(int i) {
        return ((i % 1000) % 100) / 10;
    }

    static int d(int i) {
        return ((i % 1000) % 100) % 10;
    }
    static int com(int i, int j){
        return i*10+j;
    }
    static void productTest(int i, int m, int n){
        if(i==m*n){
            P.print(i+"="+m+"*"+n);
        }

    }

    public static void main(String[] args) {
        for(int i = 1001;i<9999;i++){
            productTest(i,com(a(i),b(i)),com(c(i),d(i)));
            productTest(i,com(a(i),b(i)),com(d(i),c(i)));
            productTest(i,com(a(i),c(i)),com(b(i),d(i)));
            productTest(i,com(a(i),c(i)),com(d(i),b(i)));
            productTest(i,com(a(i),d(i)),com(b(i),c(i)));
            productTest(i,com(a(i),d(i)),com(c(i),b(i)));
            productTest(i,com(b(i),a(i)),com(c(i),d(i)));
            productTest(i,com(b(i),a(i)),com(d(i),c(i)));
            productTest(i,com(b(i),c(i)),com(d(i),a(i)));
            productTest(i,com(b(i),d(i)),com(c(i),a(i)));
            productTest(i,com(c(i),a(i)),com(d(i),b(i)));
            productTest(i,com(c(i),b(i)),com(d(i),a(i)));
        }
    }
}