枚举类型入门用 Java 5.0 以类型安全的方式表示常量[摘]

public class OldGrade {

public static final int A = 1;
public static final int B = 2;
public static final int C = 3;
public static final int D = 4;
public static final int F = 5;
public static final int INCOMPLETE = 6;
}

package com.oreilly.tiger.ch03;

public enum Grade {
A, B, C, D, F, INCOMPLETE
};

package com.oreilly.tiger.ch03;

public class Student {

private String firstName;
private String lastName;
private Grade grade;

public Student(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}

public void setFirstName(String firstName) {
this.firstName = firstName;
}

public String getFirstName() {
return firstName;
}

public void setLastName(String lastName) {
this.lastName = lastName;
}

public String getLastName() {
return lastName;
}

public String getFullName() {
return new StringBuffer(firstName)
.append(" ")
.append(lastName)
.toString();
}

public void assignGrade(Grade grade) {
this.grade = grade;
}

public Grade getGrade() {
return grade;
}
}

public void listGradeValues(PrintStream out) throws IOException {
for (Grade g : Grade.values()) {
out.println("Allowed value: '" + g + "'");
}
}

Allowed Value: 'A'
Allowed Value: 'B'
Allowed Value: 'C'
Allowed Value: 'D'
Allowed Value: 'F'
Allowed Value: 'INCOMPLETE'

public void testSwitchStatement(PrintStream out) throws IOException {
StringBuffer outputText = new StringBuffer(student1.getFullName());

switch (student1.getGrade()) {
case A:
outputText.append(" excelled with a grade of A");
break;
case B: // fall through to C
case C:
outputText.append(" passed with a grade of ")
.append(student1.getGrade().toString());
break;
case D: // fall through to F
case F:
outputText.append(" failed with a grade of ")
.append(student1.getGrade().toString());
break;
case INCOMPLETE:
outputText.append(" did not complete the class.");
break;
}

out.println(outputText.toString());
}

public void testSwitchStatement(PrintStream out) throws IOException {
StringBuffer outputText = new StringBuffer(student1.getFullName());

switch (student1.getGrade()) {
case A:
outputText.append(" excelled with a grade of A");
break;
case B: // fall through to C
case C:
outputText.append(" passed with a grade of ")
.append(student1.getGrade().toString());
break;
case D: // fall through to F
case F:
outputText.append(" failed with a grade of ")
.append(student1.getGrade().toString());
break;
case INCOMPLETE:
outputText.append(" did not complete the class.");
break;

default:
outputText.append(" has a grade of ")
.append(student1.getGrade().toString());
break;
}

out.println(outputText.toString());
}

package com.oreilly.tiger.ch03;

public enum Grade {
A, B, C, D, F, INCOMPLETE
,
WITHDREW_PASSING, WITHDREW_FAILING
};

package com.oreilly.tiger.ch03;

public enum AntStatus {
INITIALIZING,
COMPILING,
COPYING,
JARRING,
ZIPPING,
DONE,
ERROR
}

public void testEnumMap(PrintStream out) throws IOException {
// Create a map with the key and a String message
EnumMap<AntStatus, String> antMessages =
new EnumMap<AntStatus, String>(AntStatus.class);

// Initialize the map
antMessages.put(AntStatus.INITIALIZING, "Initializing Ant...");
antMessages.put(AntStatus.COMPILING,    "Compiling Java classes...");
antMessages.put(AntStatus.COPYING,      "Copying files...");
antMessages.put(AntStatus.JARRING,      "JARring up files...");
antMessages.put(AntStatus.ZIPPING,      "ZIPping up files...");
antMessages.put(AntStatus.DONE,         "Build complete.");
antMessages.put(AntStatus.ERROR,        "Error occurred.");

// Iterate and print messages
for (AntStatus status : AntStatus.values() ) {
out.println("For status " + status + ", message is: " +
antMessages.get(status));
}
}

[echo] Running AntStatusTester...
[java] For status INITIALIZING, message is: Initializing Ant...
[java] For status COMPILING, message is: Compiling Java classes...
[java] For status COPYING, message is: Copying files...
[java] For status JARRING, message is: JARring up files...
[java] For status ZIPPING, message is: ZIPping up files...
[java] For status DONE, message is: Build complete.
[java] For status ERROR, message is: Error occurred.