Java基本语句与控制流
Java
2019-12-23
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0
IF 语句
public class Main {
public static void main(String[] args) {
int monthNumber = 5;
if (monthNumber >= 1 && monthNumber <=3) {
System.out.println("You're in Quarter 1");
}
else if (monthNumber >= 4 && monthNumber <=6) {
System.out.println("You're in Quarter 2");
}
else {
System.out.println("You're not in the first half of the year!");
}
String month ="February";
if (month.equals("February")) {
System.out.println("It's the second month!");
}
}
}
Switch语句(int)
import java.io.BufferedReader;
import java.io.InputStreamReader;
public class SwitchWithInts {
public static void main(String[] args) {
String input = getInput("Enter a number between 1 and 12: ");
int month = Integer.parseInt(input); //只所以转换成Int是因为在Java 6.0的时候 switch 语句只能用在integers,shorts,bytes,以及Enums.
switch (month) {
case 1:
System.out.println("The month is January");
break; //如果去掉break,语句会继续运行下去
case 2:
System.out.println("The month is February");
break;
case 3:
System.out.println("The month is March");
break;
default:
System.out.println("You chose another month");
break;
}
}
private static String getInput(String prompt) {
BufferedReader stdin = new BufferedReader(
new InputStreamReader(System.in));
System.out.print(prompt);
System.out.flush();
try {
return stdin.readLine();
} catch (Exception e) {
return "Error: " + e.getMessage();
}
}
}
Switch语句(枚举)
新建一个Month 类
/** * Created by Haseo on 5/30/2015. */ public enum Month { JANUARY,FEBRUARY,MARCH; } 修改语句 public class SwitchWithEnums {
public static void main(String[] args) {
Month month = Month.FEBRUARY;
switch(month) {
case JANUARY:
System.out.println("The month first month");
break;
case FEBRUARY:
System.out.println("The month second month");
break;
case MARCH:
System.out.println("The month third month");
}
}
}
循环
public class Main {
static private String[] months =
{"January", "February", "March",
"April", "May", "June",
"July", "August", "September",
"October", "November", "December"};
public static void main(String[] args) {
for (int i = 0; i <months.length ; i++) {
System.out.println(months[i]);
}
//for each
for (String month:months){
System.out.println(month);
}
int counter = 0;
while (counter < months.length){
System.out.println(months[counter]);
counter++;
}
do {
System.out.println(months[counter]);
counter++;
} while (counter < months.length);
}
}
重构方法
public class Main {
public static void main(String[] args) {
doSomething();
int top = 10;
for (int i = 0; i <top ; i++) {
System.out.println("the value is "+i);
}
}
private static void doSomething (){
System.out.println("This method has been called");
}
}
选中需要重构的语句块，然后在菜单中重构为方法
结果
public class Main {
public static void main(String[] args) {
doSomething();
loopMe();
}
private static void loopMe() {
int top = 10;
for (int i = 0; i <top ; i++) {
System.out.println("the value is "+i);
}
}
private static void doSomething (){
System.out.println("This method has been called");
}
}
** 重构方法(带参数)**
以我们前面的计算器为例(Java开发环境安装及基础语句),选择代码段,然后重构
结果如下
public static void main(String[] args) { String s1 = getInput("Enter a numeric value: "); String s2 = getInput("Enter a numeric value: ");
double result = addTwoValues(s1, s2);
System.out.println("The answer is " + result);
}
private static double addTwoValues(String s1, String s2) {
double d1 = Double.parseDouble(s1);
double d2 = Double.parseDouble(s2);
return d1 + d2;
}</pre>
** 定义一个可以无限传入参数的方法**
import java.io.*;
public class Calculator {
public static void main(String[] args) {
String s1 = getInput("Enter a numeric value: ");
String s2 = getInput("Enter a numeric value: ");
double result = addTwoValues(s1, s2);
System.out.println("The answer is " + result);
double resultOfMultiple =addMultipleValues(1,2,3,4,5);
System.out.println("The answer from multiple values is " + resultOfMultiple);
}
private static double addTwoValues(String s1, String s2) {
double d1 = Double.parseDouble(s1);
double d2 = Double.parseDouble(s2);
return d1 + d2;
}
private static String getInput(String prompt) {
BufferedReader stdin = new BufferedReader(
new InputStreamReader(System.in));
System.out.print(prompt);
System.out.flush();
try {
return stdin.readLine();
} catch (Exception e) {
return "Error: " + e.getMessage();
}
}
//定义一个可以无限传入参数的方法
private static double addMultipleValues(double... values) {
double result = 0d;
for (double d : values) {
result += d;
}
return result;
}
}
重载
public class Overloading {
public static void main(String[] args){
int value1 = 5 ;
int value2 = 10 ;
int value3 = 15;
int result = addValues(value1,value2,value3);
System.out.println("The result is " + result);
String string1 = "10";
String string2 = "25";
int result2 = addValues(string1,string2);
System.out.println("The result is "+ result2);
}
private static int addValues(int int1,int int2){
return int1 + int2;
}
private static int addValues(int int1,int int2, int int3){
return int1+int2+int3;
}
private static int addValues(String val1,String val2 ){
int value1 = Integer.parseInt(val1);
int value2 = Integer.parseInt(val2);
return value1+value2;
}
}
简单计算器V2
import java.io.*;
public class Calculator2 {
public static void main(String[] args) {
String s1 = getInput("Enter a numeric value: ");
String s2 = getInput("Enter a numeric value: ");
String op = getInput("Enter 1=Add, 2=Subtract , 3=Multiply, 4=Divide : ");
int opInt = Integer.parseInt(op);
double result = 0;
switch (opInt){
case 1:
result = addValues(s1,s2);
break;
case 2:
result = subtractValues(s1,s2);
break;
case 3:
result = multiplyValues(s1,s2);
break;
case 4:
result = divideValues(s1,s2);
break;
default:
System.out.println("You entered an incorrect value:");
return;
}
System.out.println("The answer is " + result);
}
private static double addValues(String s1, String s2) {
double d1 = Double.parseDouble(s1);
double d2 = Double.parseDouble(s2);
return d1 + d2;
}
private static double subtractValues(String s1, String s2) {
double d1 = Double.parseDouble(s1);
double d2 = Double.parseDouble(s2);
return d1 - d2;
}
private static double multiplyValues(String s1, String s2) {
double d1 = Double.parseDouble(s1);
double d2 = Double.parseDouble(s2);
return d1 * d2;
}
private static double divideValues(String s1, String s2) {
double d1 = Double.parseDouble(s1);
double d2 = Double.parseDouble(s2);
return d1 / d2;
}
private static String getInput(String prompt) {
BufferedReader stdin = new BufferedReader(
new InputStreamReader(System.in));
System.out.print(prompt);
System.out.flush();
try {
return stdin.readLine();
} catch (Exception e) {
return "Error: " + e.getMessage();
}
}
}
参考资料
http://docs.oracle.com/javase/8/docs/api/
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