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  • String类的流程控制

    1:复合语句

    eg:

         public class Compound{

                   public static void main(String[]args){

                             int x=20;

                         {

                              int y=20;

                              System.out.println(y);

                              int z=245;

                              boolean b;

                              {

                                     b=y>z;

                                    System.out.println(b);

                               }

                  String world="hello java";

                  System.out.println(world);

    }

    }

    2:if条件语句

    if(布尔表达式){

            语句序列;

            }

    eg:

              int a=100;

              if(a==100){

                  System.out.println("a的值是:");

                }

       /////////////////////////////

    public class Getif{

               public static void main(String[]args){

                         int x=45,y=12;

                         if(x>y){

                          System.out.println("变量x大于y");

                             }

                          if(x<y){

                          System.out.println("变量x小于y");

                              }

       }

    }

    3:if.......else语句

    if(表达式){

           若干语句

                 }

    else{

              若干语句

    }

    if()内必须是boolean类型。有时为了编程的需要,else或if后面的“{}"中可以没有语句。

    eg:

     public class Getifelse{

                public static void main(String[]args){

                          int math=90,english=56;

                          if(math>60){

                           System.out.println("数学及格了");

                                 }

                         else

                              System.out.println("数学没有及格");

                         if(english>60){

                                System.out.println("英语及格了");

                                   }

                         else

                               System.out.println("英语未及格");

                 }

    }

    if.....else if多分支语句

      if(条件表达式1){

                    语句序列1

    }

    else if(条件表达式2){

                   语句序列2

    }

    else{

                 语句序列3

    }

    eg:

           public class GetTerm{

                       public static void main(String[]args){

                                  int x=20;

                                  if(x>30){

                                      System.out.println("x的值>30");

                                            }

                                  else if(x>10){

                                     System.out.println("x的值大于10,但小于30");

                                                  }

                                  else if(x>0){

                                     System.out.println("x的值大于0,但小于10");

                                                    }

                                   else{

                                          System.out.println("x的值小于0");

                                         }

    }

    }

    switch语句

     switch(表达式){

              case 常量值1:

                        语句模块1;

                      break;

             case 常量值2:

                     语句模块2;

                     break;

          ..............................

           default:

                   语句模块n;

                  break;

    }

    eg:

        public class Test{

                   public static void main(String[]args){

                             String str="明日科技";

                            switch(str){

                             case "明日":

                                       System.out.println(.........);

                                       break;

                            case "明日科技":

                                       System.out.println("......");

                                        break;

                             default:

                                   System.out.println("..............");

                                  }

                           }

    }

     同一个switch语句,case的常量值必须互不相同

    eg:

    public class GetSwitch{

                public static void main(String[]args){

                           int week=2;

                           switch(week){

                                   case 1:

                                              System.out.println("Monday");

                                              break;

                                 case 2:

                                            System.out.println("Tuesday");

                                            break;

                                case 3:

                                            System.out.println("Wendnesday");

                                            break;

                                default:

                                          System.out.println("I don't know");

                        }

    }

    }

    循环语句

    while语句也成判断语句,它的循环方式为利用一个条件来控制是否要继续反复执行这个语句。

    while(条件表达式){

                执行语句

    }

    eg:

         public class GetSum{

                     public static void main(String[]args){

                               int x=1;

                               int sum=0;

                               while(x<=10){

                                      sum+=x;

                                       x++;

                                       }

        System.out.println("sum="+sum);

              }

    }

    不可将while表达式的括号后面加个";"。否则进入死循环

    while(x==5);

    System.out.println("x的值为5");

    这时程序会认为要执行一个语句,而进入无限循环,java编辑器又不会报错。

    do....while循环语句

    do..while循环语句和while循环语句类似,他们之间的区别是while语句为先判断条件是否成立,再执行语句,而do...while循环语句则先执行一次循环后,再判断条件是否成立,也就是说do...while至少要执行一次。

    do{

          执行语句

    }

    while(条件表达式);

    eg:

    public class Cycle{

                 public static void main(String[]args){

                            int a=100;

                            while(a==60){

                                  System.out.println("ok1");

                                   a--;

                                  }

                           int b=100;

                          do{

                              System.out.println("ok2");

                              b--;

                             }

                             while(b==60);

                         }

    }

    运行结果:ok2

    for循环语句

    for(表达式1;表达式2;表达式3){

          语句序列           

    }

    eg:

           public class Circulate{

                      public static void main(String[]args){

                                 int sum=0;

                                 for(int i=2;i<=100;i+=2){

                                     sum+=i;

                                    }

                                 System.out.println("2到100之间的所有偶数和为:"+sum);

                         }

    foreach语句

    for(元素变量x:遍历对象obj){

                  引用了x的Java语句

        }

    eg:

       public class Repetition{

                  public static void main(String[]args){

                             int arr[]={7,10,1};

                            System.out.println("一维数组中的元素为:");

                            for(int x:arr){

                              System.out.println(x);

                               }

    }

    }

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  • 原文地址:https://www.cnblogs.com/zhouzetian/p/7354668.html
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