- 运算符与关系表达式
DEMO
// 运算符的加减
int num1 = 5, num2 = 0;
++num1;// 先加再赋值
// num1++;赋值再加
// num2--;
--num2;
System.out.println("++num1 " + num1);
System.out.println("++num2 " + num2);
// 运算符的比较
int num1 = 5, num2 = 3, num3 = 4;
boolean flag;
if (num1 < num2) {
flag = true;
System.out.println(flag + " num1=" + num1 + " < " + "num2=" + num2);
} else if (num2 < num3) {
flag = true;
System.out.println(flag + " num2=" + num2 + " < " + "num3=" + num3);
} else if (num1 < num3) {
flag = true;
System.out.println(flag + " num1=" + num1 + " < " + "num3=" + num3);
} else {
flag = false;
System.out.println(flag + " num1=" + num1 + " > " + "num3=" + num3);
}
- 逻辑运算符
! 非
&& 与
|| 或
int num1 = 5, num2 = 3, num3 = 4;
boolean flag;
if (num1 < num2 && num2 < num3) {
flag = true;
System.out.println(flag + " num1=" + num1 + " < " + "num3=" + num3);
} else if (num1 < num3) {
flag = true;
System.out.println(flag + " num1=" + num1 + " < " + "num3=" + num3);
} else {
flag = false;
System.out.println(flag + " num1=" + num1 + " > " + "num3=" + num3);
}
-
位运算符
》、《、>>>等 -
赋值运算符与表达式
int num1 = 5, num2 = 3, num3 = 4;
num1 += num1;
num2 -= num2;
num3 *= num3;
System.out.println(num1);
System.out.println(num2);
System.out.println(num3);
- 条件运算符和表达式
三个数的三目运算,最大数,最小数
// 三目运算
int num1 = 5, num2 = 3, num3 = 9; /* num4 = 6, num5 = 9, num6 = 8 */
;
/*
* int max1 = (num1>num2)?num1:num2;
* int max2 =(max1>num3)?max1:num3;
*
* int max = a>b&&a>c?a:b>c?b:c;
* int max = (a>b?a:b)>(a>c?a:c)?(a>b?a:b):(a>c?a:c);
*/
/*
* int max = (((num1 > num2) ? num1 : num2) > num3) ? ((num1 > num2) ?
* num1 : num2) : num3;
*/
int mix = (num1 < num2) ? (num1 < num3 ? num3 : num1)
: (num2 < num3 ? num2 : num3);
int max = (num1 > num2) ? (num1 > num3 ? num1 : num3)
: (num2 > num3 ? num2 : num3);
System.out.println(mix);
System.out.println(max);
- 选择
①根据输入的成绩判断是否合格
// score
public static boolean score(int s) {
if (s >= 60) {
System.out.println("合格!");
return true;
} else {
System.out.println("不合格!");
return false;
}
}
// main
public static void main(String[] args) {
System.out.println("输入成绩:");
@SuppressWarnings("resource")
Scanner sc = new Scanner(System.in);
int score = sc.nextInt();
score(score);
// if (score >= 60 && score <= 100) {
// System.out.println("合格!");
// } else if (score < 60 && score >= 0) {
// System.out.println("不合格!");
// } else {
// System.out.println("输入成绩错误!");
// }
}
②判断闰年
// 闰年 1000~2019
System.out.println("闰年 1000~2019:");
for (int Y = 1000; Y <= 2019; Y++) {
if ((Y % 4 == 0 && Y % 100 != 0) || Y % 400 == 0) {
System.out.println(Y);
}
}
③多层嵌套
// scoreMore
public static void scoreMore(int s) {
if (s >= 60) {
if (s <= 80) {
System.out.println("合格!");
} else {
System.out.println("优!");
}
} else {
if (s == 0) {
System.out.println("未参加!");
} else {
System.out.println("不合格!");
}
}
}
...
System.out.println("输入成绩:");
@SuppressWarnings("resource")
Scanner sc = new Scanner(System.in);
int score = sc.nextInt();
scoreMore(score);
④switch
// judgeScore
public static void judgeScore(int s) {
switch (s/10) {
case 10:
System.out.println("A");
break;
case 9:
System.out.println("A");
break;
case 8:
System.out.println("B");
break;
case 7:
System.out.println("C");
break;
case 6:
System.out.println("D");
break;
default:
System.out.println("E");
break;
}
}
⑤do-while|while
// sumWhile
public static void sumWhile() {
int i = 1, sum = 0;
// while (i < 10) {
// sum += i;
// System.out.println(sum);
// ++i;
// }
do {
sum += i;
// if (sum > 30 && sum < 40) {
// break;
// }
if (sum < 30 ) {
continue;// 不会执行i++
}
i++;
} while (i < 10);
System.out.println(sum);
}
⑥for
// sumFor
public static void sumFor() {
int sum = 0;
for (int i = 1; i < 10; i++) {
sum += i;
}
System.out.println(sum);
}
// MultilpyFor
public static void MultilpyFor() {
for (int i = 1; i < 10; i++) {
for (int j = 1; j <= i; j++) {
int m = i * j;
System.out.print(j + "*" + i + "=" + m+"\t");
}
System.out.println();
}
}