编码练习——Java-2-流程控制

16-08-16 来源：[db:作者]

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条件

条件语句 - if

public class Test {
    public static void main(String[] args) {
        int a = 100;
        if(a==100) {
            System.out.println("a的值是 100");
        }
    }
}

public class Test {
    public static void main(String[] args) {
        int x = 45;
        int y = 12;
        if (x>y) {
            System.out.println("变量x 大于 变量y");
        }
        if (xpublic class Test {
    public static void main(String[] args) {
        int math = 95;
        if (math>60) {
            System.out.println("数学及格了");
        } else {
            System.out.println("数学没有及格");
        }
    }
}
public class Test {
    public static void main(String[] args) {
        int x = 20;
        if(x>30) {
            System.out.println("a的值大于30");
        } else if (x>10) {
            System.out.println("a的值大于10，但小于30");
        } else if (x>0) {
            System.out.println("a的值大于0，但小于10");
        } else {
            System.out.println("a的值小于0");
        }
    }
}
条件语句 - switch
public class Test {
    public static void main(String[] args) {
        System.out.println("今天是星期几：");
        int week = 2;
        switch(week) {
        case 1:
            System.out.println("Monday");
            break;
        case 2:
            System.out.println("Tuesday");
            break;
        case 3:
            System.out.println("Wednesday");
            break;
        default:
            System.out.println("Sorry, I don't know");

        }
    }
}

实例 - 验证登录信息的合法性
import java.util.Scanner;
public class Test {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        System.out.println("请输入登录用户名：");
        String username = scan.nextLine();
        System.out.println("请输入登录密码：");
        String password = scan.nextLine();

        if (!username.equals("mr")) {
            System.out.println("用户名非法");
        } else if (!password.equals("mrsoft")) {
            System.out.println("登录密码错误");
        } else {
            System.out.println("恭喜您， 登录信息通过验证");
        }
    }
}
实例 - 为新员工分配部门
import java.util.Scanner;
public class Test {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        System.out.println("请输入新员工的姓名：");
        String name = scan.nextLine();
        System.out.println("请输入新员工应聘的编程语言：");
        String language = scan.nextLine();

        switch(language.hashCode()) {
        case 3254818:
        case 2301506:
        case 2269730:
            System.out.println("员工" + name + "被分配到Java程序开发部门。");
            break;
        case 3104:
        case 2112:
            System.out.println("员工" + name + "被分配到C#项目维护组。");
            break;
        case -709190099:
        case 955463181:
        case 9745901:
            System.out.println("员工"+name+"被分配到Asp.net程序测试部门。");
            break;
        default:
            System.out.println("本公司不需要" + language + "语言的程序开发人员。");
        }

    }
}
循环
循环语句 - while
public class Test {
    public static void main(String[] args) {
        int x = 1;
        int sum = 0;
        while (x<=10) {
            sum = sum+x;
            x++;
        }
        System.out.println("从1到10的和是：" + sum);

    }
}
循环语句 - do…while

循环体，至少执行一次。
public class Test {
    public static void main(String[] args) {
        int a = 100;
        while (a==60) { //一遍不执行
            System.out.println("Ok! a==60");
            a--;
        }

        int b = 100;
        do {    //至少执行一次
            System.out.println("Ok! b==60");
            b--;
        }
        while (b==60);

    }
}
循环语句 - for
public class Test {
    public static void main(String[] args) {
        int sum = 0;
        for(int i=1; i<=100; i+=1) {
            sum = sum+i;
        }
        System.out.println("1到100之间数的和为：" + sum);
    }
}
循环语句 -foreach
public class Test {
    public static void main(String[] args) {
        int arr[] = {7, 10, 1};
        System.out.println("一维数组中的元素分别为：");
        for (int x : arr) {
            System.out.print(x+"\t");
        }
    }
}
实例 - 使用while循环遍历数组
public class Test {
    public static void main(String[] args) {
        String[] aves = new String[] {"白露", "丹顶鹤", "黄鹂", "乌鸦", "喜鹊", "布谷鸟", "灰文鸟", "百灵鸟"};
        int index = 0;
        System.out.println("我的花园里有很多鸟，种类有：");
        while (index < aves.length) {
            System.out.print(aves[index++] + "   ");
        }
    }
}
实例 - 使用for循环输出九九乘法表
public class Test {
    public static void main(String[] args) {
        for (int i=1; i<=9; i++) {
            for (int j=1; j<=i; j++) {
                System.out.print(j + "*" + i + "=" + (i*j) + "\t");
            }
            System.out.println();
        }

    }
}
跳转语句 - break
public class Test {
    public static void main(String[] args) {
        int sum = 0;
        String flag = "从1到100之间连续整数的和是：";
        for (int i=1; i<=100; i++) {
            sum +=i;
            if(sum>1000) {
                flag = "从1到" + i + "之间连续整数的和是：";
                //跳出该层循环
                break;
            }
        }
        System.out.println(flag + sum);

    }
}

跳转语句 - continue
public class Test {
    public static void main(String[] args) {
        int i = 0;
        System.out.println("10以内的奇数有：");
        while (i<10) {
            i++;
            if (i%2 == 0) {
                continue;
            }
            System.out.print(i + "  ");
        }
    }
}
跳转语句 - return

实例 - 终止循环体（break）
public class Test {
    public static void main(String[] args) {
        System.out.println("\n----中断单层循环的例子----");
        String[] array = new String[] {"白露","丹顶鹤","黄鹂","鹦鹉","乌鸦","喜鹊","老鹰","布谷鸟","老鹰","灰文鸟","老鹰","百灵鸟"};
        for (String string : array) {
            if (string.equalsIgnoreCase("老鹰"))
                break;
            System.out.print("有：" + string + "   ");
        }

        System.out.println("\n\n----中单2层循环的例子----");
        int[][] myScores = new int[][] {{67,78,63,22,66}, {55,68,78,95,44},{95,97,92,93,81}};
        System.out.println("宝宝这次考试成绩：\n数学\t语文\t英语\t美术\t历史");
        No1: for (int[] is : myScores) {
            for (int i : is) {
                System.out.print(i + "\t");
                if(i<60) {
                    System.out.println("\n等等，" + i + "分的是什么？这个为什么不及格？");
                    break No1;
                }
            }
            System.out.println();
        }

    }
}
实例 - 循环体的过滤器（continue）
public class Test {
    public static void main(String[] args) {
        String[] array = new String[] {"白露","丹顶鹤","黄鹂","鹦鹉","乌鸦","喜鹊","老鹰","布谷鸟","老鹰","灰文鸟","老鹰","百灵鸟"};
        System.out.println("在我的花园里有很多鸟类，但是最近来了几只老鹰，请帮我把他们抓走。");
        int eagleCount = 0;
        for(String string : array) {
            if(string.equals("老鹰")) {
                System.out.println("发现一只老鹰，已经抓到笼子里。");
                eagleCount++;
                continue;
            }
            System.out.println("搜索鸟类，发现了：" + string);
        }
        System.out.println("一共捉到了：" + eagleCount + "只老鹰。");
    }
}
实例 - 使用for循环输出空心的菱形
public class Test {
    public static void main(String[] args) {
        printHollowRhombus(10);
    }

    public static void printHollowRhombus(int size) {
        if (size%2==0) 
            size++;
        for (int i=0; ii+1; j--) {
                System.out.print(" ");
            }
            for (int j=0; j<2*i+1; j++) {
                if(j==0 || j==2*i) 
                    System.out.print("*");
                else
                    System.out.print(" ");
            }
            System.out.println("");
        }
        for(int i=size/2+1; i


实例 - 使用for循环输出杨辉三角public class Test {
    public static void main(String[] args) {
        int triangle[][] = new int[8][];
        for (int i=0; i

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