[Java知识库]日撸 Java 三百行 （04-05，基础语法）

第四天：闰年的计算

1.if语句的嵌套

2.闰年的基本运算规律

3.布尔类型

package basic;

/**
 * The complex usage of the if statement.
 * 
 * @author 凤fff
 *
 */
public class LeapYear {

	/**
	 **************************
	 * The entrance of the program.
	 * 
	 * @param args Not used now.
	 **************************
	 */
	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.");
		
		tempYear = 2000 ;
		
		System.out.print(" " + tempYear + " is ");
		if ( ! isLeapYear(tempYear)) {
			System.out.print("Not ");
		} // Of if
		System.out.println("a leap year.");
		
		tempYear = 2100 ;
		
		System.out.print(" " + tempYear + " is ");
		if ( ! isLeapYear(tempYear)) {
			System.out.print("Not ");
		} // Of if
		System.out.println("a leap year.");
		
		tempYear = 2004 ;
		
		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.") ;
		tempYear = 2021 ;
		
		System.out.print(" " + tempYear + " is ");
		if ( ! isLeapYearV2(tempYear)) {
			System.out.print("Not ");
		} // Of if 
		System.out.println("a leap year.") ;
		
		tempYear = 2000 ;
		
		System.out.print(" " + tempYear + " is ");
		if ( ! isLeapYearV2(tempYear)) {
			System.out.print("Not ");
		} // Of if 
		System.out.println("a leap year.") ;
		
		tempYear = 2100 ;
		
		System.out.print(" " + tempYear + " is ");
		if ( ! isLeapYearV2(tempYear)) {
			System.out.print("Not ");
		} // Of if 
		System.out.println("a leap year.") ;
		
		tempYear = 2004 ;
		
		System.out.print(" " + tempYear + " is ");
		if ( ! isLeapYearV2(tempYear)) {
			System.out.print("Not ");
		} // Of if 
		System.out.println("a leap year.") ;
} // Of main
	/**
	 ***********************
	 * Is the given year leap?
	 * 
	 * @param paraYear The given year.
	 ***********************
	 */
	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
	
	/**
	 ***********************
	 * Is the given year leap? Replace the complex condition with a number of if.
	 *
	 * @param paraYear The given Year.
	 ***********************
	 */
	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
} // Of class LeapYear

运行结果

注意，在 isLeapYearV2 中 取余100 和取余 400 不能交换位置 判断是从上向下执行的如果上面的满足条件就不会向下执行

第五天：

1.Switch, case, break, default 用法

2. 单元测试单独使用一个方法，main 方法里面的代码越少越好

package basic;

/**
 * This is the fifth code. Names and comments should follow my style strictly.
 * 
 * @author 凤fff
 *
 */
public class SwitchStatement {

	/**
	 *********************
	 * The entrance of the program.
	 * 
	 * @param args
	 *            Not used now.
	 *********************
	 */
	public static void main(String args[]) {
		scoreToLeveTest();
	} // Of main

	/**
	 *********************
	 * Score to level.
	 * 
	 * @param paraScore
	 *            From 0 to 100.
	 * @return The level form A to F.
	 *********************
	 */
	public static char scoreToLevel(int paraScore) {
		// E stand for error, and F stands for fail.
		char resultLevel = 'E';

		// Divide by 10, the result rangs 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 scoreToLeveTest() {
		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 = 83;
		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 = 53;
		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

当 条件分支有多个 及 条件的值是整数或一个字符值 选用Switch更好