日撸代码300行：4-7天
代码来自闵老师”日撸Java三百行（01-10天，基本语法），原文链接：“https://blog.csdn.net/minfanphd/article/details/116933803
闵老师教程刚开始的时候有跟着学习，当时跟着坚持到第七天。今天对四、五、六、七四天的学习进行一个总结，接下来将从第八天继续学习。
第四天：闰年的计算
package basic;
/**
* The complex usage of the if statement. The names and comments are strictly in the original article format
*
* @author WX873
*
*/
public class LeapYear {
/**
* *************************** The entrance of the program.
*
* @param args
* Not used now. ***************************
*/
public static void main(String args[]) {
// Test isLeapYear
int tempYear = 2000;
System.out.println(tempYear + " is");
if (!isLeapYear(tempYear)) {
System.out.println("NOT");
} // of if
System.out.println("a leap year");
tempYear = 2100;
System.out.println(tempYear + " is");
if (!isLeapYear(tempYear)) {
System.out.println("NOT");
} // of if
System.out.println("a leap year");
tempYear = 2020;
System.out.println(tempYear + " is");
if (!isLeapYearV2(tempYear)) {
System.out.println("NOT");
} // of if
System.out.println("a leap year");
}// of main
public static boolean isLeapYear(int paraYear) {
if ((paraYear % 400 == 0) || (paraYear % 100 != 0) && (paraYear % 4 == 0)) {
return true;
} else {
return false;
} // of if
}// of isLeapYear
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 isLeapYear
}// of class
今天主要是if语句的使用，以及if语句的嵌套使用。if语句主要用于判断，布尔类型的返回值为0和1。今天的代码用两种方式实现了闰年的判断，一种是通过逻辑运算符，一种是通过if语句的嵌套。
逻辑运算符已经忘的差不多了，急忙百度了一下。（逻辑运算符详细介绍：http://c.biancheng.net/view/777.html）&&和&都可以表示逻辑与，但是有区别。&&又称短路与（个人觉得这个说法很有意思），&称为逻辑与。&&（短路与）只要第一个条件不成立，就不会再去判断第二个条件，直接返回false，而&会判断所有的条件。||和|的区别也类似，||只要满足一个条件，后面就不再判断了。
第五天：基本switch 语句
package basic;
/**
* This is the fifth code. The names and comments are strictly in the original article format.
*
* @author WX873
*
*/
public class SwitchStatement {
/**
* *************************************
* The entrance of the program
*
* @param args Not used now
* *************************************
*/
public static void main(String args[]) {
scoreToLevelTest();
}//of main
/**
* **************************************
* Score to level
*
* @param paraScore From 0 to 100.
* return The level from A to F.
* **************************************
*/
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';
break;
}//of switch
return resultLevel;
}//of scoreToLevel
/**
* *****************************************
* Method unit test.
* *****************************************
*/
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));
tempScore = -66;
System.out.println("Score " + tempScore + " to level is:" + scoreToLevel(tempScore));
}//of scoreToLevelTest
}//of class SwitchStatement
switch语句经常用来解决多种分支的情况。switch 语句提供了 if 语句的一个变通形式，可以从多个语句块中选择其中的一个执行。switch的详细介绍见：http://c.biancheng.net/view/738.html
default表示“默认”，就是说case所列情况都不满足，执行该分支。default 后要紧跟冒号，default 块和 case 块的先后顺序可以变动，不会影响程序执行结果。通常，default 块放在末尾，也可以省略不写。
第六天：基本for 语句
package basic;
/**
*
* This is the sixth code. The names and comments are strictly in the original article format.
*
* @author WX873
*
*/
public class ForStatement {
/**
* ********************************
* The entrance of the program.
*
* @param args Not used now.
* ********************************
*/
public static void main(String args[]) {
forStatementTest();
}//of main
/**
* ****************************
* Method unit test
* ****************************
*/
public static void forStatementTest() {
int tempN = 10;
System.out.println("1 add to " + tempN + " is:" + addToN(tempN));
tempN = 100;
System.out.println("1 add to " + tempN + " is:" + addToN(tempN));
tempN = 0;
System.out.println("1 add to " + tempN + " is:" + addToN(tempN));
tempN = 10;
int tempStepLenth = 1;
System.out.println("1 add to " + tempN + " is:" + addToNWithStepLength(tempN, tempStepLenth));
tempN = 10;
tempStepLenth = 2;
System.out.println("1 add to " + tempN + " is:" + addToNWithStepLength(tempN, tempStepLenth));
tempN = 101;
tempStepLenth = 4;
System.out.println("1 add to " + tempN + " is:" + addToNWithStepLength(tempN, tempStepLenth));
}//of forStatementTest
/**
* **************************************
* Add from 1 to N
*
* @param paraN The given upper bound.
* @return The sum
* **************************************
*/
public static int addToN(int paraN) {
int resultSum = 0;
for (int i = 1; i <= paraN; i++) {
resultSum += i;
}//of for i
return resultSum;
}//of addToN
/**
* **********************************
* Add from 1 to N with a step length.
*
* @param paraN The given upper bound.
* @param paraStepLength The given step length.
* @return The sum.
*/
public static int addToNWithStepLength(int paraN, int paraStepLength) {
int resultSum = 0;
for (int i = 1; i <= paraN; i += paraStepLength) {
resultSum += i;
}//of for i
return resultSum;
}//of addToNWithStepLength
}//of class ForStatement
for语句是程序中常用的语句，也是程序的核心，算法的时间复杂度一般根据循环语句来计算。今天的代码用for语句实现了1累加到N，和变步长1加到N两个功能。addToNWithStepLength(int paraN, int paraStepLength)方法是addToN(int paraN)的一般形式，如果步长paraStepLength为1，那么两个方法功能相同。
第七天：矩阵元素相加
package basic;
import java.util.Arrays;
/***
* This is the seventh code. The names and comments are strictly in the original article format.
*
* @author WX873
*
*/
public class MatrixAddition {
/**
* *******************************
* The entrance of the program.
*
* @param args Not used now.
* *******************************
*/
public static void main(String srgs[]) {
matrixElementSumTest();
}//of main
/**
* ******************************
* Sum the elements of a matrix.
*
* @param paraMatrix The given matrix.
* @return The sum of all its elements.
* ******************************
*/
public static int matrixElementSum(int[][] paraMatrix) {
int resultSum = 0;
for (int i = 0; i < paraMatrix.length; i++) {
for (int j = 0; j < paraMatrix[0].length; j++) {
resultSum += paraMatrix[i][j];
}//of for j
}//of for i
return resultSum;
}//of matrixElementSum
/**
* ********************************
* Unit test for respective method.
* ********************************
*/
public static void matrixElementSumTest() {
int[][] tempMatrix = new int[3][4];
for (int i = 0; i < tempMatrix.length; i++) {
for (int j = 0; j < tempMatrix[0].length; j++) {
tempMatrix[i][j] = i * 10 + j;
}//of for j
}//of for i
System.out.println("The matrix is:\r\n" + Arrays.deepToString(tempMatrix));
System.out.println("The matrix element sum is: " + matrixElementSum(tempMatrix) + "\r\n");
}//of matrixElementSumTest
}//of class MatrixAddition