Java 一些基礎語法
阿新 • • 發佈：2022-04-11
Scanner scanner = new Scanner(System.in)
scanner.hasNext進行判斷 下一個是否有元素
scanner.nextLine()全部獲取
package demo2;
import java.util.Scanner;
public class Demo01 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("使用next進行接受：");
if(scanner.hasNext()){
String str1 = scanner.nextLine();
String str2 = scanner.next();
System.out.println("輸出的內容是"+str1);
System.out.println("輸出的內容是"+str2);
}
scanner.close();
}
}
Java 中 if的使用
if判斷語句
if() //判斷括號內是否為真如果為真就繼續執行
else()//否則執行else中的語句
package demo2;
import java.util.Scanner;
public class Demo02 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int i = 0;
float f = 1.0f;
if (scanner.hasNextInt()){
i = scanner.nextInt();
System.out.println(i);
}else {
System.out.println(i+1);
}
if(scanner.hasNextFloat()){
f = scanner.nextFloat();
System.out.println(f);
}else{
System.out.println("not float");
}
scanner.close();
}
}
Java 中 while語句的使用
while(scanner.hasNextInt())中判斷
scanner.hasNextInt()是否輸入的為整數
不是則直接結束
while(true)為死迴圈
package demo2;
import java.util.Scanner;
public class demo03 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int a = 0;
int sum = 0;
while(scanner.hasNextInt()){
int x = scanner.nextInt();
a = a+1;
sum = sum+x;
}
System.out.println(sum);
}
}
java中 do while語句使用
在while判斷前會先進行do操作
沒有迴圈就會執行一次do操作
package demo2;
public class Demo07 {
public static void main(String[] args) {
int a = 0;
int sum = 0;
while(a<10){
sum = sum+a;
a++;
}
System.out.println(sum);
do{
sum = sum+a;
a++;
}while(a<10);
System.out.println(sum);
}
}
java中Switch的使用
switch是進行多次判斷
case如果和switch (grade)括號內grade相同則輸出
break為直接退出
如果沒有break會擊穿
會繼續執行下面的case條件
default為預設代表都沒有case條件成立時則執行default
package demo2;
public class Demo05 {
public static void main(String[] args) {
int A = 60;
int B = 70;
int C = 80;
int D = 90;
int E = 100;
char grade = 'c';
switch (grade){
case 'a':
System.out.println(A);
break;
case 'b':
System.out.println(A);
break;
case 'c':
System.out.println(A);
// break;
case 'd':
System.out.println(A);
// break;
case 'e':
System.out.println(A);
// break;
default:
System.out.println(E);
}
}
}
switch的進階
Jdk1.7以後switch支援對字串的比較
package demo2;
public class Demo06 {
public static void main(String[] args) {
String name = "liu";
switch (name){
case "liu":
System.out.println('1');
break;
case "li":
break;
}
}
}
Java中for語句
for( ; ; )也合法為死迴圈
for(引數；判斷；條件)
for (int i = 0; i <= 100; i++)
相當於i 從0-100的自增每次加一直到100結束迴圈
package demo2;
public class Demo08 {
public static void main(String[] args) {
// for(int a=1;a<100;a++){
// System.out.println(a);
// }
int sum = 0;
for (int i = 0; i <= 100; i++) {
sum = sum + i;
}
System.out.println(sum);
int oddsum = 0;
int evensum = 0;
for (int i = 0; i <= 100; i++) {
if(i%2==0){
oddsum = oddsum+i;
}else {
evensum = evensum+i;
}
}
System.out.println(oddsum);
System.out.println(evensum);
}
for練習
輸入0-1000之間能被5整除的數，並且3個為一行
package demo2;
public class Demo09 {
public static void main(String[] args) {
for (int i = 0; i <= 1000; i++) {
if(i%5==0){
System.out.print(i+"\t");
}
if(i%15==0){
System.out.println();
}
}
}
}
練習2 99乘法表
package demo2;
public class Demo10 {
public static void main(String[] args) {
for (int i = 1; i <=9; i++) {
for (int j = 1; j <= i; j++) {
System.out.print(i + "*" + j + "=" + i * j+"\t");
}
System.out.println();
}
}
}
練習3 列印一個三角形
package demo2;
public class Demo12 {
public static void main(String[] args) {
for (int i = 1; i <= 5; i++) {
for (int j = 5; j >= i; j--) {
System.out.print(" ");
}
for (int j = 1 ; j<=i ; j++){
System.out.print("*");
}
for (int j = 1 ; j<i ; j++){
System.out.print("*");
}
System.out.println("");
}
}
}