1.包
2.运算符
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 10 System.out.println("move = " + (move << 1)); }} 3.选择语句
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 ~ 100 System.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); }} 4.while循环
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 9 do{//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) {//67 if( 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"); else System.out.println( a +"不是素数"); }} 5.for循环
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); }} 6.标记循环
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"); } }} 7.双循环
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(); } }}