第4章 控制执行流程/4.1 true和false

标签：	作者:易学笔记  更多资料请联系微信或QQ:1776565180

 

• Java的布尔比较注意：不允许用数字进行比较true或者false，虽然这在C++中是允许的

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第4章 控制执行流程/4.2 if-else

标签：	作者:易学笔记  更多资料请联系微信或QQ:1776565180

 

• if - else

1. 概念：是控制流程最基本的语句
2. 格式：

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第4章 控制执行流程/4.3 迭代

标签：	作者:易学笔记  更多资料请联系微信或QQ:1776565180

 

• 迭代

1. 概念：是控制循环的语言
2. 包括
   1. while：
   2. do-while：
   3. for：，注意：循环中的变量要在循环模块内声明

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第4章 控制执行流程/4.3 迭代/4.3.3 逗号操作符

标签：	作者:易学笔记  更多资料请联系微信或QQ:1776565180

 

• 逗号操作符

1. • 主要用于for循环的初始化和步数修改
   • 举例：
     1. 源代码：
     2. 程序输出结果：

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第4章 控制执行流程/4.4 Foreach语法

标签：	作者:易学笔记  更多资料请联系微信或QQ:1776565180

 

• Foreach语法

1. • 是JAVA SE5中新引入的语法，是for语句的简化版，适用于数组和容器
   • 举例：
     1. 源代码：
     2. 输出结果：

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第4章 控制执行流程/4.5 break和continue

标签：	作者:易学笔记  更多资料请联系微信或QQ:1776565180

 

• 多层嵌套循环的break和continue

1. 源代码：

   //: HelloDate.java
   import java.util.*;
   //import static net.mindview.until.Print.*;
   /** the first Thinking in java example program
     * display a string and today's date
     * @author wengyongsheng 
     * @version 4.0 
   */
   public class HelloDate{
   	/**
   	* @param args array of string arguments
   	*/
     public static void main(String []args) {
     System.out.println("Hello,It's: ");
     System.out.println(new Date());
   //  print("Hello,It's: ");
   }
   }
   
   class Tank{
   	 int level;
   }
   
   class Assignment{
   	public static void main(String []args) {
   		Tank t1 = new Tank();
   		Tank t2 = new Tank();
   		t1.level = 9;
   		t2.level = 47;
   		System.out.println("1:t1.level = " + t1.level + 
   		                   " t2.level = " + t2.level);
       t1 = t2;
       System.out.println("2:t1.level = " + t1.level + 
   		                   " t2.level = " + t2.level);
   		
   		t1.level = 27;
   		System.out.println("3:t1.level = " + t1.level + 
   		                   " t2.level = " + t2.level);                   		                   
   	}
   }
   
   class Letter{
   	 char c;
   }
   
   class PassObject{
   	static void f(Letter y){
   		y.c = 'z';
   	}
   	public static void main(String []args) {
   		Letter x = new Letter();
   		System.out.println("1:x.c= " + x.c);
   		x.c = 'a';
   		System.out.println("2:x.c= " + x.c);
   		f(x);
   		System.out.println("3:x.c= " + x.c);
   	}
   }
   
   class MathOps{
   	public static void main(String []args) {
   		Random rand = new Random(47);
   		int i , j , k;
   		j = rand.nextInt(100) + 1;
   		System.out.println("j = " + j);
   		k = rand.nextInt(100) + 1;
   		System.out.println("k = " + k);
   		i = j + k;
   		System.out.println("i = " + i);
   		
   		float u , v , w;
   		u = rand.nextFloat();
   		System.out.println("u = " + u);
   		v = rand.nextFloat() ;
   		System.out.println("v = " + v);
   		w = u + v;
   		System.out.println("w = " + w);
   	}
   }
   
   class AutoInc{
   	public static void main(String []args) {
   		int i = 1;
   		System.out.println("i = " + i);
   		System.out.println("++i = " + ++i);
   		System.out.println("i++ = " + i++);
   		System.out.println("i2 = " + i);
   		System.out.println("--i = " + --i);
   		System.out.println("i-- = " + i--);
   		System.out.println("i3 = " + i);
    }
   }
   /* output
   i = 1
   ++i = 2
   i++ = 2
   i2=3
   --i = 2
   i-- = 2
   i3=1
   */
   
   class Equaivalence{
   	public static void main(String []args) {
   		Integer n1 = new Integer(47);
   		Integer n2 = new Integer(47);
   		
   		System.out.println(n1 == n2);
   		System.out.println(n1 != n2);
    }
   }
   
   class EqualsMethod{
   	public static void main(String []args) {
   		Integer n1 = new Integer(47);
   		Integer n2 = new Integer(47);
   		
   		System.out.println(n1.equals(n2));
    }
   }
   
   class Value{
   	int i ;
   }
   class EqualsMethod2{
   	public static void main(String []args) {
   		Value v1 = new Value();
   		Value v2 = new Value();
   	 System.out.println(v1.equals(v2));
    }
   }
   
   class ShortCircuit{
   	static boolean test1(int val){
   		System.out.println("test1( " + val + " )");
   		System.out.println("result: "  + (val <1) );
   		return (val < 1);
   	}
   	
   	static boolean test2(int val){
   		System.out.println("test2( " + val + " )");
   		System.out.println("result: "  + (val <1) );
   		return (val < 2);
   	}
   	
   	static boolean test3(int val){
   		System.out.println("test3( " + val + " )");
   		System.out.println("result: "  + (val <1) );
   		return (val < 3);
   	}
   	
   	
   	public static void main(String []args) {
   		
   		boolean b = test1(0) && test2(2) && test2(3);
   		System.out.println("expression is : "  + b );
   	}
   }
   
   class CommaOperator{
   	public static void main(String []args) {
   		for(int i = 1, j = i + 10; i < 5;i++,j = i*2){
   			System.out.println("i =  "  +  i + " j = "  + j);
   		}
    }
   }
   
   
   class ForEachFloat{
   	public static void main(String []args) {
   		Random rand = new Random(47);
   		float f[] = new float[10];
   		for(int i = 0; i < 10;i++){
   			f[i] = rand.nextFloat();
   		}
   		
   		for(float x:f){
   			System.out.println("x =  " + x);
   		}
   		
   		for(char c:"my name".toCharArray()){
   			System.out.println("c =  " + c);
   		}
    }
   }
   
   class LableedWhile{
   	public static void main(String []args) {
   		int i = 0;
   		outer:
   		while(true){
   			System.out.println("Outer while loop");
   			while(true){
   				i++;
   				System.out.println("i = " + i);
   				if(i == 1){
   					System.out.println("continue");
   					continue;
   				}
   				if(i == 3){
   					System.out.println("continue Outer");
   					continue outer;
   				}
   				if(i == 5){
   					System.out.println("break");
   					break;
   				}
   				if(i == 7){
   					System.out.println("break Outer");
   					break outer;
   				}
   			}
   		}
    }
   }

    

2. 输出结果：
3. 

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第4章 控制执行流程/4.8 switch

标签：	作者:易学笔记  更多资料请联系微信或QQ:1776565180

 

• 语法
  1. • 格式：
     • 注意：后面要有break
     • 举例：
       1. 源代码：

          //: HelloDate.java
          import java.util.*;
          //import static net.mindview.until.Print.*;
          /** the first Thinking in java example program
            * display a string and today's date
            * @author wengyongsheng 
            * @version 4.0 
          */
          public class HelloDate{
          	/**
          	* @param args array of string arguments
          	*/
            public static void main(String []args) {
            System.out.println("Hello,It's: ");
            System.out.println(new Date());
          //  print("Hello,It's: ");
          }
          }
          
          class Tank{
          	 int level;
          }
          
          class Assignment{
          	public static void main(String []args) {
          		Tank t1 = new Tank();
          		Tank t2 = new Tank();
          		t1.level = 9;
          		t2.level = 47;
          		System.out.println("1:t1.level = " + t1.level + 
          		                   " t2.level = " + t2.level);
              t1 = t2;
              System.out.println("2:t1.level = " + t1.level + 
          		                   " t2.level = " + t2.level);
          		
          		t1.level = 27;
          		System.out.println("3:t1.level = " + t1.level + 
          		                   " t2.level = " + t2.level);                   		                   
          	}
          }
          
          class Letter{
          	 char c;
          }
          
          class PassObject{
          	static void f(Letter y){
          		y.c = 'z';
          	}
          	public static void main(String []args) {
          		Letter x = new Letter();
          		System.out.println("1:x.c= " + x.c);
          		x.c = 'a';
          		System.out.println("2:x.c= " + x.c);
          		f(x);
          		System.out.println("3:x.c= " + x.c);
          	}
          }
          
          class MathOps{
          	public static void main(String []args) {
          		Random rand = new Random(47);
          		int i , j , k;
          		j = rand.nextInt(100) + 1;
          		System.out.println("j = " + j);
          		k = rand.nextInt(100) + 1;
          		System.out.println("k = " + k);
          		i = j + k;
          		System.out.println("i = " + i);
          		
          		float u , v , w;
          		u = rand.nextFloat();
          		System.out.println("u = " + u);
          		v = rand.nextFloat() ;
          		System.out.println("v = " + v);
          		w = u + v;
          		System.out.println("w = " + w);
          	}
          }
          
          class AutoInc{
          	public static void main(String []args) {
          		int i = 1;
          		System.out.println("i = " + i);
          		System.out.println("++i = " + ++i);
          		System.out.println("i++ = " + i++);
          		System.out.println("i2 = " + i);
          		System.out.println("--i = " + --i);
          		System.out.println("i-- = " + i--);
          		System.out.println("i3 = " + i);
           }
          }
          /* output
          i = 1
          ++i = 2
          i++ = 2
          i2=3
          --i = 2
          i-- = 2
          i3=1
          */
          
          class Equaivalence{
          	public static void main(String []args) {
          		Integer n1 = new Integer(47);
          		Integer n2 = new Integer(47);
          		
          		System.out.println(n1 == n2);
          		System.out.println(n1 != n2);
           }
          }
          
          class EqualsMethod{
          	public static void main(String []args) {
          		Integer n1 = new Integer(47);
          		Integer n2 = new Integer(47);
          		
          		System.out.println(n1.equals(n2));
           }
          }
          
          class Value{
          	int i ;
          }
          class EqualsMethod2{
          	public static void main(String []args) {
          		Value v1 = new Value();
          		Value v2 = new Value();
          	 System.out.println(v1.equals(v2));
           }
          }
          
          class ShortCircuit{
          	static boolean test1(int val){
          		System.out.println("test1( " + val + " )");
          		System.out.println("result: "  + (val <1) );
          		return (val < 1);
          	}
          	
          	static boolean test2(int val){
          		System.out.println("test2( " + val + " )");
          		System.out.println("result: "  + (val <1) );
          		return (val < 2);
          	}
          	
          	static boolean test3(int val){
          		System.out.println("test3( " + val + " )");
          		System.out.println("result: "  + (val <1) );
          		return (val < 3);
          	}
          	
          	
          	public static void main(String []args) {
          		
          		boolean b = test1(0) && test2(2) && test2(3);
          		System.out.println("expression is : "  + b );
          	}
          }
          
          class CommaOperator{
          	public static void main(String []args) {
          		for(int i = 1, j = i + 10; i < 5;i++,j = i*2){
          			System.out.println("i =  "  +  i + " j = "  + j);
          		}
           }
          }
          
          
          class ForEachFloat{
          	public static void main(String []args) {
          		Random rand = new Random(47);
          		float f[] = new float[10];
          		for(int i = 0; i < 10;i++){
          			f[i] = rand.nextFloat();
          		}
          		
          		for(float x:f){
          			System.out.println("x =  " + x);
          		}
          		
          		for(char c:"my name".toCharArray()){
          			System.out.println("c =  " + c);
          		}
           }
          }
          
          class LableedWhile{
          	public static void main(String []args) {
          		int i = 0;
          		outer:
          		while(true){
          			System.out.println("Outer while loop");
          			while(true){
          				i++;
          				System.out.println("i = " + i);
          				if(i == 1){
          					System.out.println("continue");
          					continue;
          				}
          				if(i == 3){
          					System.out.println("continue Outer");
          					continue outer;
          				}
          				if(i == 5){
          					System.out.println("break");
          					break;
          				}
          				if(i == 7){
          					System.out.println("break Outer");
          					break outer;
          				}
          			}
          		}
           }
          }
          
          class VoewlsAndConson{
          	public static void main(String []args) {
          		Random rand = new Random(47);
          		for(int i = 0; i < 100;i++){
          			int c = rand.nextInt(26) + 'a';
          			System.out.println("c = " + c);
          			switch(c){
          				case 'a':
          				case 'b':
          				case 'c': System.out.println("vowel");break;
          				case 'y':
          				case 'w':
          				case 'z':System.out.println("consonant");break;
          				default:System.out.println("xxxx");
          			}
          		}
           }
          }

           

       2. 输出结果：