常见java知识点1

**常见Java知识点**

Java是一种广泛使用的编程语言，尤其是在企业级应用开发中。以下是常见的Java知识点：

###1. Java基本数据类型Java有八个基本数据类型：

* `byte`：8位有符号整数* `short`：16位有符号整数* `int`：32位有符号整数* `long`：64位有符号整数* `float`：32位浮点数* `double`：64位浮点数* `boolean`：布尔值（true或false）
* `char`：16位Unicode字符

javapublic class BasicDataType {
 public static void main(String[] args) {
 // byte byte b =127;
 System.out.println("byte:" + b);

 // short short s =32767;
 System.out.println("short:" + s);

 // int int i =2147483647;
 System.out.println("int:" + i);

 // long long l =9223372036854775807L;
 System.out.println("long:" + l);

 // float float f =3.14f;
 System.out.println("float:" + f);

 // double double d =3.14159265358979323846;
 System.out.println("double:" + d);

 // boolean boolean bln = true;
 System.out.println("boolean:" + bln);

 // char char c = 'A';
 System.out.println("char:" + c);
 }
}

###2. Java运算符Java支持以下运算符：

* 算术运算符：`+、-、*、/、%、++、--`
* 关系运算符：`==、!=、>、<、>=、<=`
* 逻辑运算符：`&&、||、!`
* 赋值运算符：`=、+=、-=、*=、/=、%=、&=、|=、^=、<<=、>>=`

javapublic class Operator {
 public static void main(String[] args) {
 // 算术运算符 int a =10;
 int b =2;
 System.out.println("a + b:" + (a + b));
 System.out.println("a - b:" + (a - b));
 System.out.println("a * b:" + (a * b));
 System.out.println("a / b:" + (a / b));
 System.out.println("a % b:" + (a % b));

 // 关系运算符 boolean bln1 = a == b;
 boolean bln2 = a != b;
 boolean bln3 = a > b;
 boolean bln4 = a < b;
 boolean bln5 = a >= b;
 boolean bln6 = a <= b;

 System.out.println("a == b:" + bln1);
 System.out.println("a != b:" + bln2);
 System.out.println("a > b:" + bln3);
 System.out.println("a < b:" + bln4);
 System.out.println("a >= b:" + bln5);
 System.out.println("a <= b:" + bln6);

 // 逻辑运算符 boolean bln7 = a >0 && b >0;
 boolean bln8 = a >0 || b < 0;
 boolean bln9 = !bln1;

 System.out.println("a >0 && b >0:" + bln7);
 System.out.println("a >0 || b < 0:" + bln8);
 System.out.println("!bln1:" + bln9);

 // 赋值运算符 int c = a;
 System.out.println("c:" + c);

 c +=10;
 System.out.println("c +=10:" + c);

 c -=5;
 System.out.println("c -=5:" + c);

 c *=2;
 System.out.println("c *=2:" + c);

 c /=3;
 System.out.println("c /=3:" + c);
 }
}

###3. Java控制结构Java支持以下控制结构：

* 条件语句：`if、else if、else`
* 循环语句：`while、for、do-while`
* switch语句

javapublic class ControlStructure {
 public static void main(String[] args) {
 // 条件语句 int a =10;
 if (a >0) {
 System.out.println("a >0");
 } else {
 System.out.println("a <=0");
 }

 if (a ==5) {
 System.out.println("a ==5");
 } else if (a ==10) {
 System.out.println("a ==10");
 } else {
 System.out.println("a !=5 && a !=10");
 }

 // 循环语句 int b =0;
 while (b < 5) {
 System.out.println("b:" + b);
 b++;
 }

 for (int c =0; c < 5; c++) {
 System.out.println("c:" + c);
 }

 do {
 System.out.println("d:");
 int d =0;
 d++;
 } while (d < 5);

 // switch语句 char e = 'A';
 switch (e) {
 case 'A':
 System.out.println("e == A");
 break;
 case 'B':
 System.out.println("e == B");
 break;
 default:
 System.out.println("e != A && e != B");
 break;
 }
 }
}

###4. Java数组Java支持以下类型的数组：

* 一维数组* 多维数组

javapublic class Array {
 public static void main(String[] args) {
 // 一维数组 int[] a = new int[5];
 for (int i =0; i < 5; i++) {
 a[i] = i;
 }
 System.out.println("a:");
 for (int j : a) {
 System.out.print(j + " ");
 }

 // 多维数组 int[][] b = new int[2][3];
 for (int i =0; i < 2; i++) {
 for (int j =0; j < 3; j++) {
 b[i][j] = i *3 + j;
 }
 }
 System.out.println("
b:");
 for (int[] c : b) {
 for (int d : c) {
 System.out.print(d + " ");
 }
 System.out.println();
 }
 }
}

###5. Java集合Java支持以下类型的集合：

* `List`
* `Set`
* `Map`

javaimport java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;

public class Collection {
 public static void main(String[] args) {
 // List ArrayList list = new ArrayList<>();
 list.add("A");
 list.add("B");
 list.add("C");
 System.out.println("list:");
 for (String str : list) {
 System.out.print(str + " ");
 }

 // Set HashSet set = new HashSet<>();
 set.add("A");
 set.add("B");
 set.add("C");
 System.out.println("
set:");
 for (String str : set) {
 System.out.print(str + " ");
 }

 // Map HashMap map = new HashMap<>();
 map.put("A",1);
 map.put("B",2);
 map.put("C",3);
 System.out.println("
map:");
 for (String key : map.keySet()) {
 System.out.print(key + ": " + map.get(key) + " ");
 }
 }
}

以上是常见的Java知识点，包括基本数据类型、运算符、控制结构、数组和集合。这些知识点对于理解Java编程语言至关重要。