public class Operator {public static void main(String[] args) {int a = 5;System.out.println("a = " + a);//a = -a; //+   -System.out.println("a = " + a);//+ 字符串链接System.out.println("影分身" + "软件开发");System.out.println(3 + 5 + "软件开发" + 6 + 8);double b = a / 2;System.out.println("a / 2 = " + (a / 2));System.out.println("b = " + b);int weith = 10;int height = 6;double area =  1.0 / 2 * weith * height;System.out.println("area = " + area);int c = a % 3;//取余数System.out.println("c = " + c);//int d = c++;//  c++  c = c + 1; 先赋值 后自增int d = ++c;//先自增 后赋值System.out.println("d = " + d);System.out.println("c = " + c);//赋值  int e = 10; //-=  *= /= %=e += 1;// e = e + 1;System.out.println("e = " + e);//比较 > >=  5 >= 5  5 > 5  < <=  ==boolean isEquals = (1 == 1);System.out.println("isEquals = " + isEquals);int year = 2012;boolean isLeap = (year % 4 == 0 && year % 100 != 0 || year % 400 == 0); System.out.println(year +" 是否是闰年 " + isLeap);System.out.println("1 != 2 ? " + (1 != 2));//逻辑boolean isTrue = false;System.out.println("isTrue ? " + isTrue);System.out.println("!isTrue ? " + !isTrue);System.out.println("true || false ? " + (true || false));//或运算System.out.println("true && false ? " + (true && false));//与运算int score = 85;//score > 60  及格   > 70  良   > 85 优秀// javase > 60 && oracle > 70  && xml > 70 // javase > 60 || oracle > 60  || xml > 60 int move = 16;System.out.println("move = " + (move >> 3));//100   10System.out.println("move = " + (move << 1));}}

import java.util.Random;//导入类
public class IfDemo {public static void main(String[] args) {Random ran = new Random();//new 创建对象int score = ran.nextInt(101);//ran.nextInt(41) + 60;//随机数 0 ~ 100System.out.println("score = " +  score);/*if(score > 60) {//满足条件执行System.out.println("============");System.out.println("   及格了..");System.out.println("============");}*///if的第二种形式/*if(score > 60) {//满足条件执行  System.out.println("============");System.out.println("   及格了..");System.out.println("============");} else {  //不满足条件执行System.out.println("============");System.out.println("   很遗憾..");System.out.println("============");}*///多分支  匹配其中一个条件/*if( score >= 90) {System.out.println("成绩： A");} else if ( score >= 80 /*&& score < 90) {System.out.println("成绩： B");} else if ( score >= 60 /*&& score < 80) {System.out.println("成绩： C");} else {System.out.println("成绩： D");}*/switch(score / 10) {//如果匹配 下面代码执行case 10: //System.out.println("成绩： A");break;case 9: System.out.println("成绩： A");break;case 8: System.out.println("成绩： B");break;case 7: System.out.println("成绩： C");break;case 6: System.out.println("成绩： D");break;default : System.out.println("成绩： 不及格");}//三目运算符boolean isPass = ( score > 60 ? true : false);System.out.println("成绩 === " + isPass);String passed = score > 60 ? "及格" : "挂了";System.out.println("成绩 ==== " + passed);}}

import java.util.Random;
public class LoopDemo {public static void main(String[] args) {int i = 0;//计数器//循环  不满足条件不执行   可能执行0次while( i < 10 ){     System.out.println( i + " Hello World!...");//执行代码i++;//运行时 i值每次发生改变 i = 10}System.out.println( "i = " + i );i = 0; // 0  9do{//先执行 后判断  至少执行一次System.out.println( i + " 快乐!...");i++;}while (i < 10);   int a = ran.nextInt(101);System.out.println( "a = " + a );int i = 2;while( i < a) {//67if( a % i == 0) {break;//跳出循环}i++;}System.out.println( "i = " + i );if(i >= a)//正常退出循环System.out.println( a +"是素数");elseSystem.out.println( a +"不是素数");}}

import java.util.Random;
public class LoopDemo2 {public static void main(String[] args) {int k = 10; //方法中的变量 作用域 在方法中使用//i 局部变量for(int i = 0;i < 10 ; i++ ) {//三条语句System.out.println( i + " Hello World!...");}//循环嵌套/*for(int i = 0; i < 5; i++) {//k = k + i;for(int j = 0; j < 3; j++) {System.out.print(" * ");}System.out.print("\n");//输出换行}*/for(int i = 1; i < 6; i++) {for(int j = 1; j <= i; j++) {System.out.print(j + " * " + i + " = "+ i * j + "  ");}System.out.print("\n");}int sum = 0;int i;for(i = 1; i < 200; i++) {sum += i;if(sum >= 200){break;}}System.out.println("sum = " + sum);System.out.println("i = " + i);}}

import java.util.Random;
public class LoopDemo3 {public static void main(String[] args) {int sum = 0;int i,k = -1;loopi: for(i = 1; i < 200; i++) {for(int j = 1; j < 200; j++) {sum += j;if(sum >= 200){ k = j;break loopi;//指定跳出位置}}System.out.println("k = " + k);System.out.println("i = " + i);}System.out.println("sum = " + sum);System.out.println("k = " + k);for(int a = 1; a < 101; a++ ) {if( a % 3 != 0){//不能被3整除 continue;//结束本次后面代码执行}System.out.print( a + "\t");}}}

public class LoopDemo4 {public static void main(String[] args) {int sum = 0;for(int i = 1; i < 11; i++) {//控制的是行for(int j = 1; j <= i; j++) {//控制的是列System.out.print(" * ");/**/if(j > 5){ //1 2 3 4 5 6   7 8 9 10           break;//跳出内层循环}  }System.out.println();}}}