JVM学习分享-思考题

package zero.desk.stringconstantpool;

import org.junit.Test;

/**
* @author Zero
* @since 2019-09-17.
* Description:
* 当调用intern方法时,
* 如果池已经包含此字符串(equals确定),则返回池中字符串。
* 否则,将此String对象添加到池中并且返回该String对象的引用。
*/
public class StringConstantPool_Intern {

@Test
public void test1() {
String a1 = "AA";//当调用intern方法时,如果池已经包含此字符串(equals确定),则返回池中字符串。否则,将此String对象添加到池中并且返回该String对象的引用。
a1.intern();
}
}

package zero.desk.stringconstantpool;

import org.junit.Test;

/**
* @author Zero
* @since 2019-09-17.
* Description:
* /Users/zero/Code/Myself/Project/zero-Project/jvm/target/classes/zero/desk/stringconstantpool
* javap -verbose StringConstantPoolAA
* cd ../stringconstantpool
*/
public class StringConstantPoolAA {

@Test
public void test1() {
String a1 = "AA";//在常量池上创建常量AA
String a2 = "AA";//直接返回已经存在的常量AA
System.out.println(a1 == a2); //true
}

}

package zero.desk.stringconstantpool;

import org.junit.Test;

/**
* @author Zero
* @since 2019-09-17.
* Description:
* 思考题
*/
public class StringConstantPoolAAAA {

@Test
public void test1() {
String a1 = new String("AA");//在堆上创建常量AA
String a11 = a1.intern();
String a2 = "AA";//在常量池上创建常量AA
System.out.println(a1 == a2); //false
System.out.println(a1 == a11); //false
System.out.println(a11 == a2); //true
}

}

package zero.desk.stringconstantpool;

import org.junit.Test;

/**
* @author Zero
* @since 2019-09-17.
* Description:
* 思考题
*/
public class StringConstantPoolAABB {

@Test
public void test1() {
String a1 = "AA"+"BB";//在常量池上创建常量AABB
String a2 = "AABB";//在常量池上创建常量AABB
System.out.println(a1 == a2); //true
}

}

package zero.desk.stringconstantpool;

import org.junit.Test;

/**
* @author Zero
* @since 2019-09-17.
* Description:
* 思考题
*/
public class StringConstantPoolNAA {

@Test
public void test1() {
String a1 = "AA";//在常量池上创建常量AA
String a2 = new String("AA");//在堆上创建对象AA
String a3 = a2.intern();//常量池上存在常量AA,直接返回常量池上常量AA,即a1
System.out.println(a1 == a2); //false
System.out.println(a1 == a3); //true
System.out.println(a2 == a3); //false
System.out.println(System.identityHashCode(a1));
System.out.println(System.identityHashCode(a2));
}

}

package zero.desk.stringconstantpool;

import org.junit.Test;

/**
* @author Zero
* @since 2019-09-17.
* Description:
* 思考题
*/
public class StringConstantPoolNAABB {

@Test
public void test1() {
String a3 = "AA"+new String("BB"); //在堆上创建对象AABB
// String a33 = a3.intern();
String a333 = "AABB";//在常量池上创建常量AABB
System.out.println(a333 == a3); //false
//
System.out.println(System.identityHashCode(a3));
System.out.println(System.identityHashCode(a333));
}
}

package zero.desk.stringconstantpool;

import org.junit.Test;

/**
* @author Zero
* @since 2019-09-17.
* Description:
* 思考题
*/
public class StringConstantPoolNAABBi {

@Test
public void test1() {
String a3 = "AA"+new String("BB"); //在常量池上创建常量AABB
String a33 = a3.intern();
String a333 = "AABB";//在常量池上创建常量AABB
System.out.println(a333 == a3); //true
//
System.out.println(System.identityHashCode(a3));
System.out.println(System.identityHashCode(a33));
System.out.println(System.identityHashCode(a333));
}
}

package zero.desk.stringconstantpool;

import org.junit.Test;

/**
* @author Zero
* @since 2019-09-17.
* Description:
* 思考题
*/
public class StringConstantPoolNAANBB {

@Test
public void test1() {
String a3 = new String("AA")+new String("BB"); //在堆上创建对象AABB
// String a33 = a3.intern();
String a333 = "AABB";//在常量池上创建常量AABB
System.out.println(a333 == a3); //false
//
System.out.println(System.identityHashCode(a3));
System.out.println(System.identityHashCode(a333));
}
}

package zero.desk.stringconstantpool;

import org.junit.Test;

/**
* @author Zero
* @since 2019-09-17.
* Description:
* 思考题
*/
public class StringConstantPoolNAANBBi {

@Test
public void test1() {
String a3 = new String("AA")+new String("BB"); //在常量池上创建常量AABB
String a33 = a3.intern();
String a333 = "AABB";//在常量池上创建常量AABB
System.out.println(a333 == a3); //true
//
System.out.println(System.identityHashCode(a3));
System.out.println(System.identityHashCode(a33));
System.out.println(System.identityHashCode(a333));
}
}
    原文作者:DeskZero
    原文地址: https://www.cnblogs.com/DeskZero/p/11538147.html
    本文转自网络文章,转载此文章仅为分享知识,如有侵权,请联系博主进行删除。
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