Table of contents
2. Introduction of common keywords
3. Introduction of Common Modifiers
I. Introduction
In Java programming, keywords and modifiers are used to define the characteristics and behavior of program elements such as classes, methods, and variables. They provide programmers with rich functions and features to help us write efficient, structured, and safe Java code. In this article, we will explore the purpose and meaning of Java keywords and modifiers in depth, and how to select and apply them according to actual needs and programming specifications.
2. Introduction of common keywords
1. **abstract**: Used to modify a class or method to represent an abstract concept. Abstract classes cannot be instantiated directly, and subclasses need to inherit and implement abstract methods.
```java
abstract class Shape {
abstract void draw();
}
```2. **assert**: Used for assertion checking, usually used in debugging and testing phases. AssertionError is thrown when the assertion condition is false.
```java
int age = 15;
assert age >= 18 : "Must be at least 18 years old";
```3. **boolean**: Indicates Boolean type, the value is true or false.
```java
boolean isStudent = true;
```4. **break**: Used to jump out of the loop statement and end the current loop.
```java
for (int i = 0; i < 10; i++) {
if (i == 5) {
break;
}
}
```5. **byte**: Indicates an 8-bit signed integer data type.
```java
byte number = 100;
```6. **case**: used for the branch condition in the switch statement.
```java
int day = 3;
switch (day) { case 1: System.out.println("Monday"); break; case 2: System.out.println("Tuesday"); break; //. .. } ```7. **catch**: Used to catch and handle exceptions.
```java
try { // code that may cause an exception } catch (Exception e) { // exception handling code } ```
8. **char**: Indicates the 16-bit Unicode character data type.
```java
char ch = 'A';
```9. **class**: Used to define classes.
```java
class Student { // class members and methods } ```10. **continue**: Used to skip the rest of the current cycle and continue to the next cycle.
```java
for (int i = 0; i < 10; i++) { if (i == 5) { continue; } // other code in the loop body } ```
The above are just some of the common keywords, Java has many others, each with a specific purpose and function.
3. Introduction of Common Modifiers
1. **Access modifiers**: Used to control the access rights of classes, methods, and variables. There are four types of access modifiers: public, protected, private, and default.
- **public**: public access, can be accessed anywhere.
```java
public class Person { // class members and methods } ```- **protected**: protected access, can be accessed in the current class and its subclasses.
```java
protected void doSomething() { // method implementation } ```- **private**: Private access, only accessible within the current class.
```java
private int age;
```- **default**: The default access permission, that is, without any access modifiers, can only be accessed within the current package.
```java
class Animal { // class members and methods } ```2. **Non-access modifiers**: Used to change the behavior and characteristics of classes, methods, and variables, including static, final, abstract, synchronized, volatile, transient, native, strictfp, etc.
- **static**: Static modifier, used to modify class members, indicating that the member belongs to a class rather than an object.
```java
public static int count = 0;
```- **final**: final modifier, used to modify a class, method or variable, indicating that it cannot be changed or inherited.
```java
public final class Config { // class members and methods }final double PI = 3.14;
```- **abstract**: Abstract modifier, used to modify a class or method, representing an abstract concept, which cannot be instantiated directly, and requires subclasses to inherit and implement abstract methods.
```java
public abstract class Shape {
abstract void draw();
}
```- **synchronized**: Synchronization modifier, used to modify methods or code blocks to ensure security in a multi-threaded environment.
```java
public synchronized void doSomething() { // method implementation } ```- **volatile**: volatile modifier, used to modify the variable, indicating the visibility of the variable in a multi-threaded environment.
```java
public volatile boolean isRunning;
```- **transient**: Transient modifier, used to modify the variable, indicating that the variable will not be serialized.
```java
public transient String password;
```- **native**: A local modifier, used to declare a native method, indicating that the implementation of the method is provided by the native code.
```java
public native void doSomething();
```- **strictfp**: precise floating-point modifier, used to define strict precision specifications for floating-point operations.
```java
strictfp class MathCalculation { // class members and methods } ```
Four. Summary
Keywords and modifiers are important elements in Java programming, which provide programmers with rich functions and features. When writing a Java program, choosing and applying keywords and modifiers reasonably can make the code more readable, maintainable and safe. We should make good use of these keywords and modifiers according to actual needs and programming specifications to write efficient, structured, and safe Java code, thereby improving programming efficiency and quality.
I hope this article will help you understand Java keywords and modifiers. If you have any questions or comments, please leave a message in the comment area below, let us discuss and share together. Thanks for reading!