Introduction to Java first quarter _1.5_ Process Control statements

Since the choice of distance, then only the trials and hardships.

Process Control Statements

• If
• Switch
• While
• Do...while
• For
• Break
• Continue

If

package com.zhb.demo;publicclass Test1 {    publicstaticvoidmain(String[] args) {        int2;        if20){            System.out.println("num 是 偶数");        }else{            System.out.println("num 不是 偶数");        }    }}

Output Result:
Num is even

Suppose there is a problem is to determine whether a number is odd, if it is odd, the output is odd, not the output is not odd. Do you think the following code is correct?

 PackageCom.zhb.demo;ImportJava.util.Scanner; Public  class Test1 {     Public Static void Main(string[] args) {intNum Scanner in =NewScanner (system.in); System.out.println ("Please enter a number"); num = In.nextint ();if(num%2==1) {System.out.println ("num is odd"); }Else{System.out.println ("num is not an odd number"); }    }}

In fact, this code if the user input value is positive, really no problem. What if the user enters-1? -2? -3?
You know, one o'clock-1 is an odd number.

Switch

Switch to pay attention to the time

• The value of the expression in the parentheses behind the switch must be an integer or character type
• The value following the case can be a constant value or a constant expression, but it cannot be a variable or a
  Expression of a variable
• After the case matches, execute the program code in the matching block, and if you do not meet the break will continue
  Executes the contents of the next case block until the break statement is encountered or the switch statement ends
• A switch statement can contain a default branch, which must be the last branch of a switch.
  Default is performed when there are no case statements with values and variables equal.

 Public  class Test1 {     Public Static void Main(string[] args) {intnum =1;Switch(num) { Case 1: System.out.println ("Reward Apple6ps"); Case 2:; Case 3: System.out.println ("Reward pencil"); Case 4: System.out.println ("Reward Lollipop");default: System.out.println ("the hatchet."); Break; }    }}

Run results
Reward Apple6ps
Reward Pencils
Reward Lollipop
Thugs

Let's make a change to the above procedure.

 Public  class Test1 {     Public Static void Main(string[] args) {intnum =1;Switch(num) { Case 1: System.out.println ("Reward Apple6ps"); Case 2:; Case 3: System.out.println ("Reward pencil"); Break; Case 4: System.out.println ("Reward Lollipop");default: System.out.println ("the hatchet."); Break; }    }}

What will be output at this time?

While

while(判断条件){    循环操作}

Execution process

1. Determine if the condition after the while is true
2. When the condition is established, execute the operation code within the loop, and then repeat 1.2 until the loop condition is not established

Features:* First judgment, after execution *

Output 1 to 5

publicclass Test1 {    publicstaticvoidmain(String[] args) {      int i=1;      while(i<=5){          System.out.print(i+"  ");          i++;      }    }}

Do...while

do{    循环操作}while(判断条件)

Execution process:
1. Perform the cycle operation first and then determine if the loop condition is true
2. If the condition is true, continue to execute 1.2. Until the loop condition is not established.

The following execution results are 1

publicstaticvoidmain(String[] args) {      int i=1;      do{          System.out.println(i);      }while(i>100);    }

For

for(循环变量初始化; 循环条件; 循环变量变化){    循环操作}

Execution process

1. Perform the loop variable initialization section to set the initial state of the loop, which executes only once
2. The cyclic condition is judged as ture, and the Loop body code is executed; if False, exit the loop directly
3. Perform the cyclic variable change section and change the value of the loop variable so that the next judgment can be
4. Execute 2.3.4 in turn until you exit the loop

publicstaticvoidmain(String[] args) {     for (int0100; i++) {        System.out.println("这是for循环");    }    }

Let's see what this code output

 Public  class T2 {      Static BooleanFooCharc) {System.out.print (c);return true; } Public Static void Main(string[] argv) {inti =0; for(Foo (' A '); Foo' B ') && (I <2); Foo' C ')) {i++; Foo' D '); }      }  }

The result is (ABDCBDCB)

Break

Jump out of the loop

publicstaticvoidmain(String[] args) {     for (int110; i++) {        if2 ==0){            break;        }        System.out.println(i);    }    }

Only 1 is output at this time

Continue

Let the program jump immediately to the next iteration of the loop

    publicstaticvoidmain(String[] args) {     for (int110; i++) {        if2 ==0){            continue;        }        System.out.print(i);    }    }

Output results
13579

Introduction to Java first quarter _1.5_ Process Control statements