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问题:

I have a simple question:
In Java Compiler, Which type of method or variables can be defined as identifier (ID) or Keyword (reserved word)?

For following example, ID should be : add, main, a, b, c, Test1, What about print, is print an ID or keyword?

Example:

public class Test1 {
    public static int add(int a, int b) {
        return a + b;
    }
    public static void main() {
        int c;
        int a = 5;
        c = add(a, 10);
        if (c > 10)
            print("c = " + -c);
        else
            print(c);
        print("Hello World");
    }
}

回答1:

An identifier is a word used by a programmer to name a variable, method, class, or label.

        // Test1 is a class name identifier 
        public class Test1 {
                public static int add(int a, int b) { // add is identifier for a method
                      return a + b; 
                 }  

                public static void main() {
                    int c; // c is identifier for a variable
                    int a = 5;
                    c = add(a, 10);
                    if (c > 10)
                         print("c = " + -c);
                    else
                        print(c);
                    print("Hello World");
                 } 
        }

You cannot use any of the Keywords as identifiers in your java programs

print in your above program is not a Keyword, you can use print as a identifier

After using print as a identifier your code looks like this.

//Test1 is a class name identifier 
public class Test1 {
    // add is identifier for a method
    public static int add(int a, int b) {
    return a + b;
}

public static void main(String[] args) {
    int c; // c is identifier for a variable
    int a = 5;
    c = add(a, 10);
    if (c > 10)
        print("c = " + -c); // c is a String
    else
        print(c); // c is a int
    print("Hello World"); // Hello World is a String
}

/**
 * Method Overriding
 */
private static void print(int c) {
    System.out.println("In Integer Print Method "+c);
}

private static void print(String string) {
    System.out.println("In String Print Method "+string);
}

}

Also Refer :

Check Legal Identifiers in java @Peter Lawrey
List of Keywords and Reserved Words in java

回答2:

The Java keywords are part of the language, and are documented in the Java Language. You cannot use a keyword as an identifier . const and goto are reserved keywords, but not implemented. true, false, and null are literals; you still cannot use them as identifiers but they are not keywords.

From the linked Java tutorial, the keywords are