java 判断与循环语句

程序语句的三种结构

1.顺序结构

2.选择结构

3.循环结构

3.1顺序结构

3.2选择结构

举例：验证选择结构

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public class IfDemo{

public static void main(String args[]){

int x = 3; //定义变量

int y = 10; //定义变量

System.out.println("===比较开始==");

if(x>y){

System.out.println("x比y大");

}

if(x<y){

System.out.println("x比y小!");

}

}

}

if语句

if...else语句

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public class IfElseDemo{

public static void main(String args[]){

int x = 3;

if(x%2==1){

System.out.println("x是奇数");

}else{

System.out.println("x是偶数");

}

}

}

三目运算符

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public class MaxDemo{

public static void main(String args[]){

int max = 0;

int x = 3;

int y = 10;

if(x<y){

max = y;

}else

{

max = x;

}

System.out.println("最大值为：" + max);

}

}

使用三目运算符

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public class MaxDemo{

public static void main(String args[]){

int max = 0;

int x = 3;

int y = 10;

max = x>y ? x : y; //通过三目运算符

System.out.println("最大值为：" + max);

}

}

if ... else if ...else 语句

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public class MoreIfElseDemo{

public static void main(String args[]){

int x = 3;

if(x==1){

System.out.println("x的值是1");

}else if(x==2){

System.out.println("x的值是3");

}else if(x==3){

System.out.println("x的值是1");

}else{

System.out.println("x不是1,2,3中的任何一个");

}

}

}

switch语句

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public class SwitchDemo01{

//完成一个四则运算的功能

public static void main(String args[]){

int x = 3;

int y = 6;

char oper = '+';

switch(oper){

case '+':{

System.out.println("x + y = " + (x + y));

break;

}

case '-':{

System.out.println("x - y = " + (x - y));

break;

}

case '*':{

System.out.println("x * y = " + (x * y));

break;

}

case '/':{

System.out.println("x / y = " + (x / y));

break;

}

default:{

System.out.println("未知的操作");

break;

}

}

}

}

3.3循环结构

while循环

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public class WhileDemo{

public static void mian(String args[]){

int x = 1;

int sum = 0;

while(x<=10){

sum += x;

x++; //修改循环条件

}

System.out.println("1 --> 10 的累加效果为：" + sum);

}

}

do while循环

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public class DoWhileDemo{

public static void main(String args[]){

int x = 1;

int sum = 0;

do{

sum += x;

x++;

}while(x<=10);

System.out.println("1 --> 10 的累加效果为：" + sum);

}

}

for循环

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public class ForDemo{

public static void main(String args[]){

int sum = 0;

for(int x=1;x<=10;x++){

sum += x;

}

System.out.println("x --> 10 的累加效果为：" + sum);

}

}

循环嵌套操作(最好2~3层即可，不要太多，否则太占内存)

乘法表格

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public class ForNesteDemo{

public static void main(String args[]){

for(int i=1;i<=9;i++){ //控制行

for(int j=1;j<=9;j++){ //控制列

System.out.print(i+"*"+j+"="+(i*j)+"\t");

}

System.out.println();

}

}

}

使用阶梯形状变化

public class ForNesteDemo{

public static void main(String args[]){

for(int i=1;i<=9;i++){ //控制行

for(int j=1;j<=i;j++){ //控制列

System.out.print(i+"*"+j+"="+(i*j)+"\t");

}

System.out.println();

}

}

}

3.4终端语句

break语句

可以中断for循环语句====以后的操作都不在执行了

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public class BreakDemo{

public static void main(String args[]){

for(int i=1;i<10;i++){

if(i==3){

break;

}

System.out.println("i = " + i);

}

}

}

continue语句

只中断一次循环的执行

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public class ContinueDemo{

public static void main(String args[]){

for(int i=1;i<10;i++){

if(i==3){

continue;

}

System.out.println("i = " + i);

}

}

}