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protected訪問權限

1、protected的類、類屬變量及方法，包內的任何類，及包外的那些繼承了此類的子類才能訪問；

注意：子類如處于不同的包，則相互間不能訪問繼承自父類的方法。

所有不能訪問的方法都已經被注釋：

package packageA;
2

public class Base {
4

public String publicStr = "publicString";
5

protected String protectedStr = "protectedString";
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String defaultStr = "defaultString";
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private String privateStr = "privateString";
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public void print() {
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System.out.println("packageA.Base has access to");
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System.out.println(" " + publicStr);
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System.out.println(" " + protectedStr);
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System.out.println(" " + defaultStr);
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System.out.println(" " + privateStr);
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Base b = new Base(); // -- other Base instance
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System.out.println(" b." + b.publicStr);
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System.out.println(" b." + b.protectedStr);
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System.out.println(" b." + b.defaultStr);
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System.out.println(" b." + b.privateStr);
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}
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}
23

--------------------------------------------------------------------------------
25

package packageA;
27

public class SubA extends Base {
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public void print() {
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System.out.println("packageA.SubA has access to");
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System.out.println(" " + publicStr + " (inherited from Base)");
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System.out.println(" " + protectedStr + " (inherited from Base)");
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System.out.println(" " + defaultStr + " (inherited from Base)");
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// -- not accessible - private elements are even not inherited
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// System.out.println(privateStr);
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Base b = new Base(); // -- other Base instance
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System.out.println(" b." + b.publicStr);
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System.out.println(" b." + b.protectedStr);
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System.out.println(" b." + b.defaultStr);
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// -- not accessible
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// System.out.println(b.privateStr);
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}
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}
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--------------------------------------------------------------------------------
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package packageA;
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public class AnotherA {
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public void print() {
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System.out.println("packageA.AnotherA has access to");
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Base b = new Base();
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System.out.println(" b." + b.publicStr);
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System.out.println(" b." + b.protectedStr);
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System.out.println(" b." + b.defaultStr);
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// System.out.println(b.privateStr);
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}
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}
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--------------------------------------------------------------------------------
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package packageB;
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import packageA.Base;
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public class SubB extends Base {
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public void print() {
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System.out.println("packageB.SubB has access to");
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System.out.println(" " + publicStr + " (inherited from Base)");
70

// -- protectedStr is inherited element -> accessible
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System.out.println(" " + protectedStr + " (inherited from Base)");
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// -- not accessible
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// System.out.println(defaultStr);
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// System.out.println(privateStr);
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Base b = new Base(); // -- other Base instance
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System.out.println(" b." + b.publicStr);
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// -- protected element, which belongs to other object -> not accessible
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// System.out.println(b.protectedStr);
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// -- not accessible
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// System.out.println(b.defaultStr);
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// System.out.println(b.privateStr);
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}
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}
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--------------------------------------------------------------------------------
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package packageB;
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import packageA.Base;
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public class AnotherB {
93

public void print() {
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System.out.println("packageB.AnotherB has access to");
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Base b = new Base();
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System.out.println(" b." + b.publicStr);
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// -- not accessible
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// System.out.println(b.protectedStr);
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// System.out.println(b.defaultStr);
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// System.out.println(b.privateStr);
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}
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}
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--------------------------------------------------------------------------------
105

106

import packageA.*;
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import packageB.*;
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// -- testing class
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public class TestProtection {
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public static void main(String[] args) {
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// -- all classes are public, so class TestProtection
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// -- has access to all of them
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new Base().print();
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new SubA().print();
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new AnotherA().print();
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new SubB().print();
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new AnotherB().print();
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}
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}
121

posted on 2009-02-21 19:39 何克勤閱讀(539) 評論(0) 編輯收藏所屬分類: J2SE

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