java 的 return 是指標

本題目不是很正確，但是我想說的是java的return 類引用是指標。下面一段程式碼

public class RetTest
{
    private TestEntity tsEt;
	private String tsStr;
	private int tsI;

    public RetTest()
    {
		tsI = 0;
		tsStr = "A";
        tsEt = new TestEntity();
    }

	public int GetI()
	{
		return tsI;
	}

	public int I1()
    {
		tsI = 1;
		return tsI;
	}	

	public int I2()
	{
		tsI = 2;
		return tsI;
	}

	public String GetStr()
	{
		return tsStr;
	}

	public String Str1()
	{
	    tsStr = "B";
		return tsStr;
	}

	public String Str2()
	{
		tsStr = "C";
		return tsStr;
	}

    public TestEntity GetEntity()
    {
        return tsEt;
    }

    public TestEntity Entity1()
    {
        //TestEntity tsEt1 = new TestEntity();
        tsEt.SetI(1);
        tsEt.SetIRef(new Integer(1));
        return tsEt;    
    }

    public TestEntity Entity2()
    {
        tsEt.SetI(2);
        tsEt.SetIRef(new Integer(2));
        return tsEt;
    }

   // public static void main(String[] args)
	public static void main(String[] args)
    {
        RetTest retTest = new RetTest();

		int Itest = retTest.GetI();
		System.out.println("I: " + Itest);

		int Itest1 = retTest.I1();
		System.out.println("I: " + Itest);
		System.out.println("I1: " + Itest1);

		int Itest2 = retTest.I2();
		System.out.println("I: " + Itest);
		System.out.println("I1: " + Itest1);
		System.out.println("I2: " + Itest2);

		//-----------------------------------------------------

		String str = retTest.GetStr();
		System.out.println("Str: " + str);

		String str1 = retTest.Str1();
		System.out.println("Str: " + str);
		System.out.println("Str1: " + str1);

		String str2 = retTest.Str2();
		System.out.println("Str: " + str);
		System.out.println("Str1: " + str1);
		System.out.println("Str2: " + str2);

		//-----------------------------------------------------

        TestEntity testEt = retTest.GetEntity();
        System.out.println("testEt -> Integer: " + testEt.GetIRef() + ", i:" + testEt.GetI());

        TestEntity testEt1 = retTest.Entity1();
        System.out.println("testEt -> Integer: " + testEt.GetIRef() + ", i:" + testEt.GetI());
        System.out.println("testEt1 -> Integer: " + testEt1.GetIRef() + ", i:" + testEt1.GetI());

        TestEntity testEt2 = retTest.Entity2();
        System.out.println("testEt -> Integer: " + testEt.GetIRef() + ", i:" + testEt.GetI());
        System.out.println("testEt1 -> Integer: " + testEt1.GetIRef() + ", i:" + testEt1.GetI());
        System.out.println("testEt2 -> Integer: " + testEt2.GetIRef() + ", i:" + testEt2.GetI()); 


		System.out.println("testEt = testEt1: " + (testEt == testEt1));
		System.out.println("testEt = testEt2: " + (testEt == testEt2));
		System.out.println("testEt1 = testEt2: " + (testEt1 == testEt2));
    }

}

class TestEntity
{
    private Integer iRef;
    private int i;

    public void SetI(int i)
    {
        this.i = i;
    }

    public int GetI()
    {
        return i;
    }

    public void SetIRef(Integer iRef)
    {
         this.iRef = iRef;
    }

    public Integer GetIRef()
    {
        return iRef;
    }
}

返回的結果為：

I: 0
I: 0
I1: 1
I: 0
I1: 1
I2: 2
Str: A
Str: A
Str1: B
Str: A
Str1: B
Str2: C
testEt -> Integer: null, i:0
testEt -> Integer: 1, i:1
testEt1 -> Integer: 1, i:1
testEt -> Integer: 2, i:2
testEt1 -> Integer: 2, i:2
testEt2 -> Integer: 2, i:2
testEt = testEt1: true
testEt = testEt2: true
testEt1 = testEt2: true

可以看出int 是值型別，返回的是值的copy
TestEntity 是一個類， 它返回的情況：

testEt -> Integer: null, i:0
testEt -> Integer: 1, i:1
testEt1 -> Integer: 1, i:1
testEt -> Integer: 2, i:2
testEt1 -> Integer: 2, i:2
testEt2 -> Integer: 2, i:2
testEt = testEt1: true
testEt = testEt2: true
testEt1 = testEt2: true

可以清楚的看出return的就是指標內容

而String型別的怎麼看上去像是基本型別的一樣呢？String也是類啊！
因為在String的物件池裡，"A"、"B"、"C"三個字串都是並沒有存在的，這樣每次String型別的物件每次=的時候相當於都要建立了一個String的物件。當然就如Str = new String("A); Str1 = new String("B"); Str2 = new String("C");這是三個不同的類當然在堆中的地址也是不同的。
由於String物件池的特性，有時候也會產生這樣的情況。如果修改一些程式碼

...
          public String Str1()
	{
	    tsStr = "A"; //把“B”改成“A”
	    return tsStr;
	}
...

新增

......
System.out.println("Str = Str1: " + (str == str1));
System.out.println("Str = Str2: " + (str == str2));
System.out.println("Str1 = Str2: " + (str1 == str2));
......

關於String測試的部分就會是：

Str: A
Str: A
Str1: A
Str: A
Str1: A
Str2: C
Str = Str1: true
Str = Str2: false
Str1 = Str2: false

這時候“Str = Str1: true”，要理解這個其實對java中的String很熟悉的話也是很好理解的。因為“A” 在物件池裡已經存在了，這時候=的時候後面是“A”的話，物件的指標就會指向已經存在的“A”，而不在新建物件。
return 針對物件是指標，知道的這點編寫函式的時候，尤其類中全域性變數，在被返回的時候有可能多個函式都返回，這樣就要注意了，return的只不過是指標！