java 01~~05

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文章目录

前言Day01——从“Hello Would”开始吧Day02——基本算术操作

（四则运算）代码如下：运行结果 Day03——基本if语句

（求绝对值）代码如下：运行结果小结 Day04——if语句嵌套

（闰年的计算）小结 Day05——基本switch语句

（判断分数的对应等级）运行结果小结

前言

Day01——从“Hello Would”开始吧

public class HelloWould {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
        System.out.println("Hello Would!");
	}// Of main
}// Of class HelloWould

Day02——基本算术操作（四则运算）代码如下：

public class math {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
        int tempFirstInt = 15,
            tempSecondInt = 4,
            tempResultInt;
        double tempFirstDouble= 1.2,
        	   tempSecondDouble = 3.5,
        	   tempResultDouble;
        //  +
        tempResultInt = tempFirstInt + tempSecondInt;
        tempResultDouble = tempFirstDouble + tempSecondDouble;
        
        System.out.println(tempFirstInt + " + " + tempSecondInt + " = " + tempResultInt);
		System.out.println(tempFirstDouble + " + " + tempSecondDouble + " = " + tempResultDouble);
        //  -
		tempResultInt = tempFirstInt - tempSecondInt;
        tempResultDouble = tempFirstDouble - tempSecondDouble;
        
        System.out.println(tempFirstInt + " - " + tempSecondInt + " = " + tempResultInt);
		System.out.println(tempFirstDouble + " - " + tempSecondDouble + " = " + tempResultDouble);
		//  *（乘）
		tempResultInt = tempFirstInt * tempSecondInt;
        tempResultDouble = tempFirstDouble * tempSecondDouble;
        
        System.out.println(tempFirstInt + " * " + tempSecondInt + " = " + tempResultInt);
		System.out.println(tempFirstDouble + " * " + tempSecondDouble + " = " + tempResultDouble);
		//  /（除）
		tempResultInt = tempFirstInt / tempSecondInt;
        tempResultDouble = tempFirstDouble / tempSecondDouble;
        
        System.out.println(tempFirstInt + " / " + tempSecondInt + " = " + tempResultInt);
		System.out.println(tempFirstDouble + " / " + tempSecondDouble + " = " + tempResultDouble);
		//  %（取余）
        tempResultInt = tempFirstInt % tempSecondInt;
		System.out.println(tempFirstInt + " % " + tempSecondInt + " = " + tempResultInt);
	}//Of main 

}//Of class math

运行结果

Day03——基本if语句（求绝对值）代码如下：

public class HelloWould {
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int tempNumber1 = 6;
		System.out.println("The absolute value of " + tempNumber1 + " is " + abs(tempNumber1));
		int tempNumber2 = -8;
		System.out.println("The absolute value of " + tempNumber2 + " is " + abs(tempNumber2));
	}// Of main
	
	public static int abs(int paraValue) {
		if (paraValue >= 0) {
			return paraValue;
		} else {
			return -paraValue;
		} // Of if
	}// Of abs
}

运行结果

小结

if-else语句在Java编程中较为常用，是常见的多分支语句。上段程序用于求一个整型数的绝对值，取绝对值的部分单独作为一个静态方法，通过引用方法传入实参，可让方法返回一个值，这个值即为所给数的绝对值。

Day04——if语句嵌套（闰年的计算）

   //闰年的判断条件：可被4整除但不能同时被100整除，或者能被400整除
    public class LeapYear {
    public static void main(String args[]) {
    
   // Test isLeapYear
		int tempYear = 2021;
		System.out.print("" + tempYear + " is ");
		if (!isLeapYear(tempYear)) {
			System.out.print("NOT ");
		} // Of if
		System.out.println("a leap year.");
		
  // Test isLeapYearV2
		System.out.println("Now use the second version.");
		
		System.out.print("" + tempYear + " is ");
		if (!isLeapYearV2(tempYear)) {
			System.out.print("NOT ");
		} // Of if
		System.out.println("a leap year.");
		
  //下面是包含双分支if—-else的方法
    public static boolean isLeapYear(int paraYear) {
		if ((paraYear % 4 == 0) && (paraYear % 100 != 0) || (paraYear % 400 == 0)) {
			return true;
		} else {
			return false;
		} // Of if
	}// Of isLeapYear
	
   //下面是包含多分支if-else的方法
      public static boolean isLeapYearV2(int paraYear) {
		if (paraYear % 4 != 0) {
			return false;
		} else if (paraYear % 400 == 0) {
			return true;
		} else if (paraYear % 100 == 0) {
			return false;
		} else {
			return true;
		} // Of if
	}// Of isLeapYearV2
}

小结

1.在一个分支中又完整的嵌套了另一个完整的分支结构，里面的分支结构称为内层分支，外面的分支结构称为外层分支。
2.嵌套最好不要超过3层，否则可读性差

Day05——基本switch语句（判断分数的对应等级）

package basic;


public class SwitchStatement {

	public static void main(String args[]) {
		scoreToLevelTest();
	}// Of main

	
	public static char scoreToLevel(int paraScore) {
		// E stands for error, and F stands for fail.
		char resultLevel = 'E';

		// Divide by 10, the result ranges from 0 to 10
		int tempDigitalLevel = paraScore / 10;

		// The use of break is important.
		switch (tempDigitalLevel) {
		case 10:
		case 9:
			resultLevel = 'A';
			break;
		case 8:
			resultLevel = 'B';
			break;
		case 7:
			resultLevel = 'C';
			break;
		case 6:
			resultLevel = 'D';
			break;
		case 5:
		case 4:
		case 3:
		case 2:
		case 1:
		case 0:
			resultLevel = 'F';
			break;
		default:
			resultLevel = 'E';
		}// Of switch

		return resultLevel;
	}// of scoreToLevel

	
	public static void scoreToLevelTest() {
		int tempScore = 100;
		System.out.println("Score " + tempScore + " to level is: " + scoreToLevel(tempScore));

		tempScore = 91;
		System.out.println("Score " + tempScore + " to level is: " + scoreToLevel(tempScore));

		tempScore = 82;
		System.out.println("Score " + tempScore + " to level is: " + scoreToLevel(tempScore));

		tempScore = 75;
		System.out.println("Score " + tempScore + " to level is: " + scoreToLevel(tempScore));

		tempScore = 66;
		System.out.println("Score " + tempScore + " to level is: " + scoreToLevel(tempScore));

		tempScore = 52;
		System.out.println("Score " + tempScore + " to level is: " + scoreToLevel(tempScore));

		tempScore = 8;
		System.out.println("Score " + tempScore + " to level is: " + scoreToLevel(tempScore));

		tempScore = 120;
		System.out.println("Score " + tempScore + " to level is: " + scoreToLevel(tempScore));
	}// Of scoreToLevelTest
}// Of class SwitchStatement

运行结果

小结

1.switch(表达式)中，表达式的数据类型应该和case后的常量类型一致，或者是可以自动转换成可以相互比较的类型，如常量为int，而输入是字符。
2.switch(表达式)中，表达式的返回值必须是：（byte，short，int，char,String,enum（枚举））
3.case子句中的值必须是常量，而不能是变量
4.可以没有default
5.break语句执行后跳出该switch。如果没有break，则程序会顺序执行到switch结尾

java 01~~05

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