编码练习——Java-2-流程控制

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");        }    }}
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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 (x<y) {            System.out.println("变量x 小于 变量y");        }    }}
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public 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");        }    }}
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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");        }    }}
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• 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");        }    }}
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• 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");        }    }}
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• 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。");        }    }}
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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);    }}
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• 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);    }}
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• 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);    }}
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• 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");        }    }}
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• 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++] + "   ");        }    }}
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• 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();        }    }}
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• 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);    }}
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• 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 + "  ");        }    }}
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• 跳转语句 - return

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• 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();        }    }}
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• 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。");    }}
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• 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; i<size/2+1; i++) {            for(int j=size/2; j>i+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<size; i++) {            for(int j=0; j<i-size/2; j++) {                System.out.print(" ");            }            for(int j=0; j<2*size-1-2*i; j++) {                if(j==0 || j==2*(size-i-1))                    System.out.print("*");                else                    System.out.print(" ");            }            System.out.println("");        }    }}
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• 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<triangle.length; i++) {            triangle[i] = new int[i+1];            for(int j=0; j<=triangle[i].length-1; j++) {                if(i==0||j==0||j==triangle[i].length-1)                    triangle[i][j] = 1;                else                    triangle[i][j] = triangle[i-1][j] + triangle[i-1][j-1];                System.out.print(triangle[i][j] + "\t");            }            System.out.println();        }    }}from: http://blog.csdn.net/xuezhisdc/article/details/52185229