20230516 java.lang.StringBuilder

介绍

• java.lang.StringBuilder
• public final class StringBuilder extends AbstractStringBuilder implements java.io.Serializable, Comparable<StringBuilder>, CharSequence
• 此类提供与 StringBuffer 兼容的 API，但不保证线程安全
• append 方法总是在构建器的末尾添加这些字符； insert 方法在指定点添加字符

构造函数

• public StringBuilder()
• public StringBuilder(int capacity)
• public StringBuilder(String str)
• public StringBuilder(CharSequence seq)

API

编辑等操作：

• append
• delete, deleteCharAt
• insert
• replace
• reverse
• toString

其他：

• charAt
• chars
• compareTo
• indexOf, lastIndexOf
• isEmpty
• length
• subSequence, subString

代码示例

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

public class StringBuilderTest {

    @Test
    void testAppend() {
        StringBuilder builder = new StringBuilder("Hello");
        builder.append(" world");
        Assertions.assertEquals("Hello world", builder.toString());
    }

    @Test
    void testInsert() {
        StringBuilder builder = new StringBuilder("1234");
        builder.insert(2, "56");
        Assertions.assertEquals("125634", builder.toString());
    }

    @Test
    void testDelete() {
        StringBuilder builder = new StringBuilder("abcdefg");
        builder.delete(1, 3);
        Assertions.assertEquals("adefg", builder.toString());
    }

    @Test
    void testReverse() {
        StringBuilder builder = new StringBuilder("abcde");
        builder.reverse();
        Assertions.assertEquals("edcba", builder.toString());
    }

    @Test
    void testReplace() {
        StringBuilder builder = new StringBuilder("abcde");
        builder.replace(1, 3, "12");
        Assertions.assertEquals("a12de", builder.toString());
    }
    
}