内部类可以访问其所有实例成员,实例字段和其封闭类的实例方法。
参考如下实例 -
class Outer {
private int value = 2017;
public class Inner {
public void printValue() {
System.out.println("Inner: Value = " + value);
}
} // Inner class ends here
public void printValue() {
System.out.println("Outer: Value = " + value);
}
public void setValue(int newValue) {
this.value = newValue;
}
}
public class Main {
public static void main(String[] args) {
Outer out = new Outer();
Outer.Inner in = out.new Inner();
out.printValue();
in.printValue();
out.setValue(2018);
out.printValue();
in.printValue();
}
}
上面的代码生成以下结果。
Outer: Value = 2017
Inner: Value = 2017
Outer: Value = 2018
Inner: Value = 2018
示例-1
以下代码显示如何访问内部类的内部变量。
public class Main {
public static void main(String[] args) {
Outer out = new Outer();
Outer.Inner in = out.new Inner();
out.printValue();
in.printValue();
out.setValue(3);
out.printValue();
in.printValue();
}
}
class Outer {
private int value = 1;
public class Inner {
private int value = 2;
public void printValue() {
System.out.println("Inner: Value = " + value);
}
} // Inner class ends here
public void printValue() {
System.out.println("Outer: Value = " + value);
}
public void setValue(int newValue) {
this.value = newValue;
}
}
上面的代码生成以下结果。
Outer: Value = 1
Inner: Value = 2
Outer: Value = 3
Inner: Value = 2
Inner类中的this关键字
以下代码显示如何在内部类中使用关键字 - this
。
class Outer {
private int value = 1;
class QualifiedThis {
private int value = 2;
public void printValue() {
System.out.println("value=" + value);
System.out.println("this.value=" + this.value);
System.out.println("QualifiedThis.this.value=" + QualifiedThis.this.value);
}
public void printHiddenValue() {
int value = 2;
System.out.println("value=" + value);
System.out.println("this.value=" + this.value);
System.out.println("QualifiedThis.this.value=" + QualifiedThis.this.value);
}
}
public void printValue() {
System.out.println("value=" + value);
System.out.println("this.value=" + this.value);
}
}
public class Main {
public static void main(String[] args) {
Outer outer = new Outer();
Outer.QualifiedThis qt = outer.new QualifiedThis();
System.out.println("printValue():");
qt.printValue();
System.out.println("printHiddenValue():");
qt.printHiddenValue();
outer.printValue();
}
}
上面的代码生成以下结果。
printValue():
value=2
this.value=2
QualifiedThis.this.value=2
printHiddenValue():
value=2
this.value=2
QualifiedThis.this.value=2
value=1
this.value=1
隐藏变量
如果实例变量名称被隐藏,必须使用关键字this
或类名称以及关键字this
限定其名称。
class TopLevelOuter {
private int v1 = 100;
// Here, only v1 is in scope
public class InnerLevelOne {
private int v2 = 200;
// Here, only v1 and v2 are in scope
public class InnerLevelTwo {
private int v3 = 300;
// Here, only v1, v2, and v3 are in scope
public class InnerLevelThree {
private int v4 = 400;
// Here, all v1, v2, v3, and v4 are in scope
}
}
}
}
从外部类
以下代码显示如何从外部类引用变量。
public class Test{
private int value = 1;
public class Inner {
private int value = 2;
public void printValue() {
System.out.println("Inner: Value = " + value);
System.out.println("Outer: Value = " + Test.this.value);
}
} // Inner class ends here
public void printValue() {
System.out.println("\nOuter - printValue()...");
System.out.println("Outer: Value = " + value);
}
public void setValue(int newValue) {
System.out.println("\nSetting Outer's value to " + newValue);
this.value = newValue;
}
}