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public class Main {
public static void main(String[]args) {
// 2进制表示--10进制为3
System.out.println(0b0011);
// 16进制表示--10进制为14
System.out.println(0xe);
// 8进制表示--10进制为8
System.out.println(010);
// 可以在数字中加下划线便于阅读
System.out.println(100_100_100);
// 长整型可以加一个'L'作为后缀
System.out.println(1000000000L);
// float类型的浮点数后面使用后缀'F'，double类型的浮点数后面使用后缀'D'，
System.out.println(0.01F);
System.out.println(0.01D);
}
}
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import java.util.Arrays;
public class Main {
public static void main(String[]args) {
int[] arr = {1,2,3,4,5};
int[] cloneArr = arr;
int[] p = Arrays.copyOf(arr,arr.length);
arr[1] = 10;
for (int num: arr) {
System.out.printf(num + " ");
}
System.out.println();
for (int num: cloneArr) {
System.out.printf(num + " ");
}
System.out.println();
for (int num: p) {
System.out.printf(num + " ");
}
}
}
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每一行的数据长度可以不相等，创建多维数组时必须指定行数
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import java.util.Arrays;
public class Main {
public static void main(String[]args) {
final int MAX = 10;
// 指定行数
int[][] arr = new int[MAX][];
// 分配行的长度
for (int i = 0; i < MAX; i++) {
arr[i] = new int[i+1];
}
for (int i = 0; i < MAX; i++) {
for (int j = 0; j <= i; j++) {
arr[i][j] = j+1;
}
}
for (int[] row : arr) {
for (int val: row) {
System.out.print(val + " ");
}
System.out.println();
}
// 快速打印二维数组的值
System.out.println(Arrays.deepToString(arr));
}
}
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交换数组的任意两行
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import java.util.Arrays;
public class Main {
public static void main(String[]args) {
int[][] arr = {{1,2,3},{4,5,6,7}};
int[] tmp = arr[0];
arr[0] = arr[1];
arr[1] = tmp;
System.out.println(Arrays.deepToString(arr));
}
}
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二维数组复制
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public class Main {
public static void main(String[]args) {
int[][] arr = {{1,2,3},{4,5,6,7}};
// 长度为行数
int[][] arr_copy = Arrays.copyOf(arr,2);
System.out.println(Arrays.deepToString(arr_copy));
}
}
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String ans = String.join(",","hello","are","you","ok"); // 使用逗号分隔字符串
System.out.println("hello".equalsIgnoreCase("HEllo")); // true 不区分大小写比较
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import java.io.Console;
public class Main {
public static void main(String[]args) {
Console console = System.console();
String str = console.readLine("User name: ");
char[] password = console.readPassword("password: ");
System.out.println(str);
for (int i = 0; i < password.length; i++) {
System.out.println(password[i]);
}
}
}
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对第i个参数多次不同的格式化输出
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import java.util.Date;
public class Main {
public static void main(String[]args) {
String name = "Alice";
int age = 18;
String message = String.format("Hello %s,Next year you will be %d",name,age+1);
System.out.println(message);
System.out.printf("%.2f%%\n",20*100/100.0);
System.out.printf("%1$s %2$tB %2$te, %2$tY\n", "Due date:", new Date());
System.out.printf("%1$.2f,%1$.3f,%1$.4f",100/3.0);
}
}
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标签必须放在希望跳出的最外层循环之前， 并且必须紧跟一个冒号:
可以将一个标签放在想要跳到的语句块之前，类似于goto的作用
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import java.util.Scanner;
public class Main {
public static void main(String[]args) {
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
label:
for (int i = 0; i < n; i++) {
if (i == 10) {
System.out.println(i);
break label;
} else {
System.out.println(i);
}
}
}
}
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import java.math.BigInteger;
public class Main {
public static void main(String[]args) {
// 使用字符串创建大整数
BigInteger bigInteger = new BigInteger("11111111111111111111111111111111111111111111111111111111");
// 最大只支持long
BigInteger bigInteger1 = BigInteger.valueOf(111111111);
// 四则运算+取模
System.out.println(bigInteger.add(bigInteger1));
System.out.println(bigInteger.subtract(bigInteger1));
System.out.println(bigInteger.multiply(BigInteger.valueOf(1111111)));
System.out.println(bigInteger.divide(new BigInteger("11111111")));
System.out.println(bigInteger.mod(bigInteger1));
}
}
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